<Page> SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K Current Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): JANUARY 16, 2004 TC PIPELINES, LP (Exact name of registrant as specified in its charter) DELAWARE 000-26091 52-2135448 (State or other jurisdiction (Commission (I.R.S. Employer of incorporation) File Number) Identification No.) 110 TURNPIKE ROAD, SUITE 203 01581 WESTBOROUGH, MASSACHUSETTS (Zip Code) (Address of principal executive offices) (508) 871-7046 (Registrant's telephone number, including area code) <Page> ITEM 7. FINANCIAL STATEMENTS AND EXHIBITS. (c) Exhibits Exhibit 99.1 - News Release of TC PipeLines, LP (the "Partnership") entitled "TC PipeLines, LP Fourth Quarter Distribution", dated January 16, 2004. ITEM 9. REGULATION FD DISCLOSURE. On January 16, 2004 the Partnership issued a news release announcing its fourth quarter distribution. The information in Item 9 of this report is being furnished, not filed, pursuant to Regulation FD. Accordingly, the information in Item 9 of this report will not be incorporated by reference into any registration statement filed by the Partnership under the Securities Act of 1933, as amended, unless specifically identified therein as being incorporated therein by reference. SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized. TC PipeLines, LP By: TC PipeLines GP, Inc., its general partner Dated: January 16, 2004 By: /s/ Ronald J. Turner ------------------------------------- Ronald J. Turner President and Chief Executive Officer -2- <Page> EXHIBIT INDEX Exhibit 99.1 News Release of TC PipeLines, LP entitled "TC PipeLines, LP Fourth Quarter Distribution", dated January 16, 2004. -3-