WASHINGTON (AP) — America's foremost labor federation is asking Congress to block the "fast track" authority that President Barack Obama seeks to advance trade deals being negotiated with numerous nations.

But the Chamber of Commerce says the authority would significantly expand U.S. exports and jobs.

AFL-CIO president Richard Trumka tells a Senate committee the fast-track legislation has pitfalls. The bill would let Congress reject or endorse -- but not amend -- proposed trade deals.

In prepared remarks, Trumka says the bill would handcuff Congress' ability to influence trade agreements.

But Chamber of Commerce President Thomas Donohue's written testimony says fast-track authority is crucial to ratifying deals that would help U.S. producers reach big foreign markets.

Obama is likely to send Congress a 12-nation Pacific-rim trade proposal if he wins fast-track approval.