WASHINGTON, May 7 (Reuters) - The U.S. Senate will begin debate next week on legislation granting President Barack Obama "fast-track" negotiating authority key to completing a sweeping Pacific trade pact, Senate Majority Leader Mitch McConnell said on Thursday.
McConnell, the chamber's top Republican, set a procedural vote for Tuesday that will provide an initial test of the Senate's support for the Trade Promotion Authority legislation that many of Obama's fellow Democrats oppose.
McConnell will have to find 60 votes in the 100-member Senate in favor of limiting debate on whether to formally begin work on the fast-track trade bill.
Under fast-track, Obama can complete negotiations on the 12-nation Trans-Pacific Partnership free trade deal knowing that the U.S. Congress can only approve or reject the measure, and not impose changes to the deal.
U.S. labor unions have launched a vigorous campaign to defeat the bill, arguing that free-trade deals have cost Americans jobs and failed to provide adequate environmental protections in foreign countries.
Senate Democratic leader Harry Reid, meanwhile, has put the Senate on notice that he could slow progress on the trade legislation, saying that two other bills, one to provide highway construction funding and another dealing with a domestic surveillance program, were more pressing.
Reid also is a vocal opponent of the fast-track trade bill.
(Reporting by Richard Cowan; Editing by Richard Chang)