Photographer: SeongJoon Cho/Bloomberg

Trade Promotion Authority, the legislation that is considered essential for trade deals to make it through Congress, cleared the Senate Finance Committee late last night after many hours of debate over hundreds of proposed amendments. One of them, little noticed at the time, could throw a big wrench in the process going forward.

The amendment, offered by Sen. Bob Menendez (D-N.J.), would prevent Congress from "fast tracking" any treaties with countries considered by the State Department to be far out of compliance with international standards on human trafficking. Currently, that list includes Malaysia, which is also a party to the Trans-Pacific Partnership, a massive trade deal with Pacific Rim countries that is in the final stages of negotiation.

Sen. Robert Menendez (D-N.J.) (Photo by Chip Somodevilla/Getty Images)

It is soon to say that will torpedo the overall plan to give the president the capacity to wrap up negotiations on the TPP and proceed to an up-or-down vote in Congress, which Trade Promotion Authority requires. But it shows that although advocates of the trade deal are celebrating passage of "fast track" through committee, the road could still be bumpy to final approval.

Going forward, the Senate could strip out the amendment on the floor. Or, Trade Promotion Authority could pass with the amendment intact, and the Trans Pacific Partnership would have to go through regular order in Congress, which would make the deal very difficult to conclude given the opposition by so many Democrats. Finally, the U.S. government could pressure Malaysia to not sign the trade treaty until it comes into compliance with human trafficking regulations, which would allow the deal to be fast tracked.

The human trafficking amendment passed 16-10, with significant support from both Republicans and Democrats. It got a yes vote from  Sen. Ron Wyden (D-Ore.), Trade Promotion Authority's main proponent among Senate liberals. Menendez voted against the ultimate bill, but says that the amendment was an attempt to incentivize countries to better combat human trafficking.

Ranking Member Ron Wyden (D-OR), left, and Chairman Orrin Hatch (R-UT), right(Photo by Gabriella Demczuk/Getty Images)

"When you’re in the middle of negotiating with trade partners, the reality is that if they decide they cannot or will not live up to a certain element of the agreement, they can fix their act and be eligible for it later on," Menendez said in an interview. Furthermore, he said, the Senate might have problems voting against an anti-trafficking provision in trade legislation.

"I would be shocked if the committee, having had a bipartisan vote, and the Senate having had a 99-0 vote on the human trafficking bill that absorbed so much time, would try to strip it out," Menendez said. "I think there would be strong opposition to any such attempts."

Sen. Sherrod Brown (D-Ohio), who has been a strident opponent of Trade Promotion Authority and offered scores of amendments to the bill, said the issue of Malaysia should hold up the treaty.

“Like so many amendments to fast track, this amendment represented a genuine effort to improve American trade policy," he said. "Our trade policy shouldn’t reward countries that are the worst perpetrators of human trafficking. We just secured a bipartisan victory in the Senate to crack down on human trafficking. Our trade policy shouldn’t undermine this, even if that means removing Malaysia from TPP or preventing the flawed TPP deal from being fast tracked.”

But a spokeswoman for Sen. Orrin Hatch (R-Utah), the chairman of the Senate Finance Committee, responded to questions about the amendment by suggesting there is more room to work out tweaks to the bill as it moves through Congress.

"While the Finance Committee’s action on a TPA renewal bill and other trade initiatives was significant, it is still the first step in the legislative process," said Hatch spokeswoman Julia Lawless. "As these measures move through the Congress, we’ll continue with our efforts to ensure a strong trade bill is enacted into law."

For its part, the White House -- which is strongly backing TPA -- argued that allowing Malaysia to join the trade agreement would be a better way of incentivizing it to crack down on human trafficking.

"The Administration is committed to working with members each step of the way to ensure that the final bill is consistent with the President's commitment to only sign trade agreements that put in place historic new protections for human rights, environmental, and labor standards and level the playing field for our workers," said an administration official. "Blocking agreements with countries like Malaysia removes an important and effective incentive for them to improve their practices."

This article has been updated with a statement from the White House.