Sen Charles Schumer said he worries that new trade deals will not help middle class incomes.
He also said the United States must do more to prevent China from keeping its currency's value artificially low, which enhances Chinese exports and dampens imports.
Schumer addressed his remarks to US Trade Representative Michael Froman, who made the administration's pitch to the Senate Finance Committee.
Froman said Congress must return "trade promotion authority" to the White House in order to cut important trade deals with Pacific-rim nations and others. That power, sometimes called "fast-track" authority, allows presidents to send proposed trade agreements to Congress for yes or no votes, with no amendments.
Several anti-trade protesters interrupted Froman's opening remarks, and were ushered out by police. Some mentioned the 1994 North American Free Trade Agreement, which many labor groups disdain.
Froman said his negotiating team is pushing India and other countries to include greater safeguards for workers and the environment as they seek new trade agreements with the United States.
President Barack Obama, in his State of the Union speech, said he needs enhanced negotiating authority to cut a new trade deal with Japan and 10 other Pacific nations, before moving to other possible pacts.
But Froman said his team is pushing China on several issues, "including protection and enforcement of trade secrets and other intellectual property rights.
