Improving labor rights in Mexico must be a central issue in reaching a new North American trade deal or the U.S. Congress won’t approve it, two Democratic lawmakers said on the eve of a new round of Nafta talks.

“Labor rights in Mexico is not an issue that can be sidestepped,” Representatives Bill Pascrell of New Jersey and Sandy Levin of Michigan said. “It is the central issue that must be addressed in any rewrite of Nafta. Failure by Mexico to stop suppressing its workers’ wages will not only be an obstacle for a new NAFTA, it will be a death knell for any deal passing Congress.”

Levin and Pascrell seek to put labor issues front and center as a new round of negotiations to rework the North American Free Trade Agreement begins on Sunday. It’s a view that, while coming from the minority party in Congress, may strike a chord with President Donald Trump, who’s made better conditions for Mexican workers a requirement for revising the deal.

A new bill in Mexico has been criticized by U.S. labor unions, which say it would encourage more jobs to flee south of the border, and the Democrats referenced that bill in their statement.

The statement includes a letter signed Jan. 23 by more than 180 members of Congress to U.S. Trade Representative Robert Lighthizer, saying that any new Nafta agreement must have strong and binding provisions addressing Mexico’s labor conditions. It states that the current objectives in Nafta renegotiations don’t do “nearly enough” to address the problem.

Mexico’s new bill, which is scheduled for debate in the current congressional session, “would limit freedom of association and promote precarious work, likely driving Mexican wages even lower and encouraging further outsourcing of American and Canadian jobs,” AFL-CIO President Richard Trumka wrote in a letter addressed to Lighthizer and dated Dec. 12.

Mexico’s labor ministry said in a statement that a portion of the new bill, which unions said left subcontractors with no protection, has been stricken from the draft by lawmakers.