Starboard Value SC 13D/A WAUSAU PAPER / Starboard Value ownership change

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO § 240.13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO

§ 240.13d-2(a)

(Amendment No. 6)1

Wausau Paper Corp.

(Name of Issuer)

Common Stock, no par value

(Title of Class of Securities)

943315101

(CUSIP Number)

JEFFREY C. SMITH

STARBOARD VALUE LP

830 Third Avenue, 3rd Floor

New York, New York 10022

(212) 845-7977

STEVEN WOLOSKY, ESQ.

OLSHAN FROME WOLOSKY LLP

Park Avenue Tower

65 East 55th Street

New York, New York 10022

(212) 451-2300

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

October 12, 2012

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box ¨.

Note:  Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits.  See § 240.13d-7 for other parties to whom copies are to be sent.

_______________

1              The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON STARBOARD VALUE AND OPPORTUNITY MASTER FUND LTD
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION CAYMAN ISLANDS
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 4,584,886
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 4,584,886
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 4,584,886
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 9.3%
14	TYPE OF REPORTING PERSON CO

2

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON STARBOARD VALUE AND OPPORTUNITY S LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 1,128,750
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 1,128,750
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,128,750
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 2.3%
14	TYPE OF REPORTING PERSON OO

3

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON STARBOARD VALUE LP
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 7,100,000
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 7,100,000
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 7,100,000
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 14.4%
14	TYPE OF REPORTING PERSON PN

4

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON STARBOARD VALUE GP LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 7,100,000
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 7,100,000
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 7,100,000
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 14.4%
14	TYPE OF REPORTING PERSON OO

5

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON STARBOARD PRINCIPAL CO LP
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 7,100,000
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 7,100,000
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 7,100,000
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 14.4%
14	TYPE OF REPORTING PERSON PN

6

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON STARBOARD PRINCIPAL CO GP LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 7,100,000
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 7,100,000
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 7,100,000
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 14.4%
14	TYPE OF REPORTING PERSON OO

7

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON JEFFREY C. SMITH
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION USA
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER - 0 -
	8	SHARED VOTING POWER 7,100,000
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 7,100,000
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 7,100,000
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 14.4%
14	TYPE OF REPORTING PERSON IN

8

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON MARK MITCHELL
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION USA
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER - 0 -
	8	SHARED VOTING POWER 7,100,000
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 7,100,000
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 7,100,000
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 14.4%
14	TYPE OF REPORTING PERSON IN

9

CUSIP NO. 943315101

1	NAME OF REPORTING PERSON PETER A. FELD
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION USA
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER - 0 -
	8	SHARED VOTING POWER 7,100,000
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 7,100,000
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 7,100,000
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 14.4%
14	TYPE OF REPORTING PERSON IN

10

CUSIP NO. 943315101

The following constitutes Amendment No. 6 to the Schedule 13D filed by the undersigned (“Amendment No. 6”).  This Amendment No. 6 amends the Schedule 13D as specifically set forth herein.

Item 3. Source and Amount of Funds or Other Consideration.

Item 3 is hereby amended and restated to read as follows:

The Shares purchased by each of Starboard V&O Fund and Starboard LLC and held in the Starboard Value LP Account were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted, as set forth in Schedule A, which is incorporated by reference herein.  The aggregate purchase price of the 4,584,886 Shares beneficially owned by Starboard V&O Fund is approximately $35,036,686, excluding brokerage commissions.  The aggregate purchase price of the 1,128,750 Shares beneficially owned by Starboard LLC is approximately $7,532,746, excluding brokerage commissions. The aggregate purchase price of the 1,386,364 Shares held in the Starboard Value LP Account is approximately $11,886,766, excluding brokerage commissions.

Item 5. Interest in Securities of the Issuer.

Items 5(a) -5(c) are hereby amended and restated to read as follows:

The aggregate percentage of Shares reported owned by each person named herein is based upon 49,322,921 Shares outstanding, as of July 31, 2012, which is the total number of Shares outstanding as reported in the Issuer’s Quarterly Report on Form 10-Q, filed with the Securities and Exchange Commission on August 9, 2012.

A. Starboard V&O Fund

(a) As of the close of business on October 16, 2012, Starboard V&O Fund beneficially owned 4,584,886 Shares.

Percentage: Approximately 9.3%.

(b) 1. Sole power to vote or direct vote: 4,584,886

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 4,584,886

4. Shared power to dispose or direct the disposition: 0

(c) The transactions in the Shares by Starboard V&O Fund since the filing of Amendment No. 5 to the Schedule 13D are set forth in Schedule A and are incorporated herein by reference.

B. Starboard LLC

(a) As of the close of business on October 16, 2012, Starboard LLC beneficially owned 1,128,750 Shares.

Percentage: Approximately 2.3%.

11

CUSIP NO. 943315101

(b) 1. Sole power to vote or direct vote: 1,128,750

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 1,128,750

4. Shared power to dispose or direct the disposition: 0

(c) The transactions in the Shares by Starboard LLC since the filing of Amendment No. 5 to the Schedule 13D are set forth in Schedule A and are incorporated herein by reference.

C. Starboard Value LP

(a) As of the close of business on October 16, 2012, 1,386,364 Shares were held in the Starboard Value LP Account. Starboard Value LP, as the investment manager of Starboard V&O Fund and the Manager of Starboard LLC, may be deemed the beneficial owner of the (i) 4,584,886 Shares owned by Starboard V&O Fund, (ii) 1,128,750 Shares owned by Starboard LLC and (iii) 1,386,364 Shares held in the Starboard Value LP Account.

Percentage: Approximately 14.4%.

(b) 1. Sole power to vote or direct vote: 7,100,000

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 7,100,000

4. Shared power to dispose or direct the disposition: 0

(c) The transactions in the Shares by Starboard Value LP through the Starboard Value LP Account and on behalf of Starboard V&O Fund and Starboard LLC since the filing of Amendment No. 5 to the Schedule 13D are set forth in Schedule A and are incorporated herein by reference.

D. Starboard Value GP

(a) Starboard Value GP, as the general partner of Starboard Value LP, may be deemed the beneficial owner of the (i) 4,584,886 Shares owned by Starboard V&O Fund, (ii) 1,128,750 Shares owned by Starboard LLC and (iii) 1,386,364 Shares held in the Starboard Value LP Account.

Percentage: Approximately 14.4%.

(b) 1. Sole power to vote or direct vote: 7,100,000

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 7,100,000

4. Shared power to dispose or direct the disposition: 0

(c) Starboard Value GP has not entered into any transactions in the Shares since the filing of Amendment No. 5 to the Schedule 13D.  The transactions in the Shares on behalf of Starboard V&O Fund and Starboard LLC and through the Starboard Value LP Account since the filing of Amendment No. 5 to the Schedule 13D are set forth in Schedule A and are incorporated herein by reference.

12

CUSIP NO. 943315101

E. Principal Co

(a) Principal Co, as a member of Starboard Value GP, may be deemed the beneficial owner of the (i) 4,584,886 Shares owned by Starboard V&O Fund, (ii) 1,128,750 Shares owned by Starboard LLC and (iii) 1,386,364 Shares held in the Starboard Value LP Account.

Percentage: Approximately 14.4%.

(b) 1. Sole power to vote or direct vote: 7,100,000

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 7,100,000

4. Shared power to dispose or direct the disposition: 0

(c) Principal Co has not entered into any transactions in the Shares since the filing of Amendment No. 5 to the Schedule 13D.  The transactions in the Shares on behalf of Starboard V&O Fund and Starboard LLC and through the Starboard Value LP Account since the filing of Amendment No. 5 to the Schedule 13D are set forth in Schedule A and are incorporated herein by reference.

F. Principal GP

(a) Principal GP, as the general partner of Principal Co, may be deemed the beneficial owner of the (i) 4,584,886 Shares owned by Starboard V&O Fund, (ii) 1,128,750 Shares owned by Starboard LLC and (iii) 1,386,364 Shares held in the Starboard Value LP Account.

Percentage: Approximately 14.4%.

(b) 1. Sole power to vote or direct vote: 7,100,000

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 7,100,000

4. Shared power to dispose or direct the disposition: 0

(c) Principal GP has not entered into any transactions in the Shares since the filing of Amendment No. 5 to the Schedule 13D.  The transactions in the Shares on behalf of Starboard V&O Fund and Starboard LLC and through the Starboard Value LP Account since the filing of Amendment No. 5 to the Schedule 13D are set forth in Schedule A and are incorporated herein by reference.

G. Messrs. Smith, Mitchell and Feld

(a) Each of Messrs. Smith, Mitchell and Feld, as a member of Principal GP and as a member of each of the Management Committee of Starboard Value GP and the Management Committee of Principal GP, may be deemed the beneficial owner of the (i) 4,584,886 Shares owned by Starboard V&O Fund, (ii) 1,128,750 Shares owned by Starboard LLC and (iii) 1,386,364 Shares held in the Starboard Value LP Account.

Percentage: Approximately 14.4%.

(b) 1. Sole power to vote or direct vote: 0

2. Shared power to vote or direct vote: 7,100,000

3. Sole power to dispose or direct the disposition: 0

4. Shared power to dispose or direct the disposition: 7,100,000

(c) None of Messrs. Smith, Mitchell or Feld has entered into any transactions in the Shares since the filing of Amendment No. 5 to the Schedule 13D.  The transactions in the Shares on behalf of Starboard V&O Fund and Starboard LLC and through the Starboard Value LP Account since the filing of Amendment No. 5 to the Schedule 13D are set forth in Schedule A and are incorporated herein by reference.

13

CUSIP NO. 943315101

SIGNATURES

After reasonable inquiry and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated:  October 16, 2012

STARBOARD VALUE AND OPPORTUNITY MASTER FUND LTD By: Starboard Value LP,        its investment manager   STARBOARD VALUE AND OPPORTUNITY S LLC By: Starboard Value LP,        its manager   STARBOARD VALUE LP By: Starboard Value GP LLC,        its general partner STARBOARD VALUE GP LLC By: Starboard Principal Co LP,        its member   STARBOARD PRINCIPAL CO LP By: Starboard Principal Co GP LLC,        its general partner   STARBOARD PRINCIPAL CO GP LLC

By:	/s/ Jeffrey C. Smith
	Name:	Jeffrey C. Smith
	Title:	Authorized Signatory

/s/ Jeffrey C. Smith

JEFFREY C. SMITH

Individually and as attorney-in-fact for Mark Mitchell and Peter A. Feld

14

CUSIP NO. 943315101

SCHEDULE A

Transactions in the Shares Since the Filing of Amendment No. 5 to the Schedule 13D

Shares of Common Stock Purchased/(Sold) Price Per Share($) Date of Purchase/Sale

STARBOARD VALUE AND OPPORTUNITY MASTER FUND LTD
9,998	8.5727	10/03/2012
20,806	8.5797	10/03/2012
19,220	8.6409	10/03/2012
19,120	8.7097	10/04/2012
36,830	8.6729	10/04/2012
1,325	8.7500	10/05/2012
68,573	8.8747	10/05/2012
170,890	8.6500	10/11/2012
11,049	8.5917	10/12/2012
2,210	8.5773	10/12/2012

STARBOARD VALUE AND OPPORTUNITY S LLC
2,246	8.5727	10/03/2012
4,675	8.5797	10/03/2012
4,318	8.6409	10/03/2012

STARBOARD VALUE LP

(Through the Starboard Value LP Account)

3,575	8.5727	10/03/2012
7,440	8.5797	10/03/2012
6,873	8.6409	10/03/2012
6,837	8.7097	10/04/2012
13,170	8.6729	10/04/2012
474	8.7500	10/05/2012
24,520	8.8747	10/05/2012
61,110	8.6500	10/11/2012
3,951	8.5917	10/12/2012
790	8.5773	10/12/2012