EXHIBIT 5.1 LAW OFFICES STEARNS WEAVER MILLER WEISSLER ALHADEFF & SITTERSON, P.A. MUSEUM TOWER 150 WEST FLAGLER STREET MIAMI, FLORIDA 33130 --------- MIAMI (305) 789-3200 o BROWARD (954) 463-5440 FAX (305) 789-3395 E. RICHARD ALHADEFF ALICE R. HUNEYCUTT PATRICIA A. REDMOND OWEN S. FREED LOUISE JACOWITZ ALLEN RICHARD B. JACKSON ELIZABETH G. RICE SENIOR COUNSEL STUART D. AMES THEODORE A. JEWELL GLENN M. RISSMAN LAWRENCE J. BAILIN MICHAEL I. KEYES CARL D. ROSTON DAVID M. SMITH PATRICK A. BARRY TEDDY D. KLINGHOFFER DAVID A. ROTHSTEIN LAND USE CONSULTANT AMANDA C. BARRY ROBERT T. KOFMAN BETTY CHANG ROWE SHAWN BAYNE THOMAS A. LASH STEVEN D. RUBIN LISA K. BENNETT PAUL TAGER LEHR CLAIRE SAADY TAMPA OFFICE SUSAN FLEMING BENNETT VERNON L. LEWIS MIMI L. SALL SUITE 2200 LISA K. BERG WENDELL T. LOCKE NICOLE S. SAYFIE SUNTRUST FINANCIAL CENTRE MARK J. BERNET KEVIN B. LOVE RICHARD E. SCHATZ 401 EAST JACKSON STREET HANS C. BEYER JOY SPILLIS LUNDEEN LESTER E. SEGAL TAMPA, FLORIDA 33602 MARTIN G. BURKETT GEOFFREY MacDONALD MARTIN S. SIMKOVIC CLAIRE BAILEY CARRAWAY MICHAEL C. MARSH CURTIS H. SITTERSON (813) 223-4800 ELLEN I. CHO BRIAN J. McDONOUGH RONNI D. SOLOMON SETH THOMAS CRAINE ANTONIO R. MENENDEZ MARK D. SOLOV PETER L. DESIDERIO FRANCISCO J. MENENDEZ EUGENE E. STEARNS FORT LAUDERDALE OFFICE MARK P. DIKEMAN ALISON W. MILLER JENNIFER D. STEARNS SUITE 1900 SHARON QUINN DIXON VICKI LYNN MONROE BRADFORD SWING 200 EAST BROWARD BOULEVARD ALAN H. FEIN HAROLD D. MOOREFIELD, JR. ANNETTE TORRES FORT LAUDERDALE, FLORIDA 33301 ANGELO M. FILIPPI JOHN N. MURATIDES DENNIS R. TURNER ANDREA F. FISHER JOHN K. OLSON RONALD L. WEAVER (954) 462-9500 ROBERT E. GALLAGHER, JR. ROBERT C. OWENS ROBERT I. WEISSLER CHAVA E. GENET JAY P. W. PHILP PATRICIA G. WELLES LATASHA A. GETHERS DARRIN J. QUAM THOMAS H. WILLIAMS, JR. PATRICIA K. GREEN NICOLE R. RAMIREZ MARTIN B. WOODS JOSEPH K. HALL JOHN M. RAWICZ February 11, 1998 MasTec, Inc. 3155 N.W. 77th Avenue Miami, Florida 33122-1205 Dear Sirs: We have acted as counsel to MasTec, Inc., a Delaware corporation (the "Company"), in connection with the proposed exchange (the "Exchange") by the Company of 7 3/4% Series B Senior Subordinated Notes Due 2008 ("New Notes") for an equal principal amount of its outstanding 7 3/4% Senior Subordinated Notes Due 2008 ("Old Notes"). In connection with the proposed Exchange, we have examined the Company's Certificate of Incorporation and By-laws, as presently in effect, the Company's relevant corporate proceedings, the draft Registration Statement on Form S-4 covering the proposed Exchange (the "Registration Statement"), including the Prospectus filed as a part of the Registration Statement, the Indenture dated February 4, 1998, in respect of the Old Notes and the New Notes (the "Indenture"), and such other documents, records, certificates of public officials, statutes and decisions as we considered necessary to express the opinions contained herein. In the examination of such documents, we have assumed the genuineness of all signatures and the authenticity of all documents submitted to us as originals and the conformity to the original documents of all documents submitted to us as certified or photostatic copies. STEARNS WEAVER MILLER WEISSLER ALHADEFF & SITTERSON, P.A. MASTEC, INC. February 11, 1998 Page 2 We understand that the New Notes are to be issued to the holders of the Old Notes in the Exchange and are to be available for resale by such holders, all in the manner described in the Prospectus, which is a part of the Registration Statement, and in the Indenture. Based on the foregoing, we are of the opinion that: 1. The issuance of the New Notes to the holders of the Old Notes pursuant to the terms of the Exchange and the Indenture have been duly authorized by proper corporate action of the Company. 2. When the Registration Statement shall have been declared effective by order of the Securities and Exchange Commission and the New Notes have been duly issued to and exchanged for the Old Notes, all in accordance with the terms of the Exchange, the Indenture and the Registration Statement, such New Notes will be validly issued and will constitute binding obligations of the Company, subject, as to enforcement (i) to any applicable bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and similar laws relating to or affecting creditors' rights and remedies generally and (ii) to general principles of judicial discretion and equity, including principles of commercial reasonableness, good faith and fair dealing (regardless of whether enforcement is sought in a proceeding at law or in equity or in a bankruptcy proceeding and except that (i) rights to contribution or indemnification may be limited by the laws, rules or regulations of any governmental authority or agency thereof or by public policy and (ii) waivers as to usury, stay or extension laws may be unenforceable). We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to any reference to us in the Prospectus which is a part hereof. Sincerely, STEARNS WEAVER MILLER WEISSLER ALHADEFF & SITTERSON, P.A. SWM/dr STEARNS WEAVER MILLER WEISSLER ALHADEFF & SITTERSON, P.A.