Democrats are digging in and demanding that Mexico make far-reaching changes to its labor laws before they agree to back President Trump's U.S.-Mexico-Canada agreement on trade.

Mexico is currently in the process of passing reforms, but it is unclear if they will satisfy the lawmakers.

In a letter Friday to U.S. Trade Representative Robert Lighthizer, a group of 86 Democrats led by Rep. Bill Pascrell, D-N.J., said they didn't think that Mexico's current proposed reform efforts went far enough. The letter was sent the day after Mexico's lower house passed a package of reforms aimed at addressing Democrats' concerns.

"We commend you for negotiating [the reform requirements] in the USMCA, which holds potential to address some key concerns if properly monitored and enforced," the Democrats said. "However, Mexico has not yet enacted, much less implemented, its labor law reform as required by ... USMCA."

The lawmakers said that while there had proposed legislation in Mexico that "meets and even exceeds the obligations in some respects, [it] must not be allowed to become a game of multiple choice, in which the Parties can pick and choose which obligations they want to enforce."

The Mexican legislature's lower house approved a labor reform bill Thursday aimed at addressing the Democrats' concerns. "It’s a reform for labor justice and will democratize unions. One of its main objectives is to transform the labor justice system," Mario Degado, the lower house's majority leader, told reporters Thursday. The reforms are expected to be voted on by the upper house next week.

Friday's letter to Lighthizer did not directly reference that vote, however, and a person with knowledge of the letter's drafting said it was mostly written prior to the vote. House Speaker Nancy Pelosi, D-Calif., and numerous other Democratic lawmakers who have raised concerns about USMCA's Mexico labor rights language did not respond to requests for comment from the Washington Examiner regarding the passage of the reform.

The White House is pushing for a vote on USMCA, which would replace the 1993 North American Free Trade Agreement, by this summer in order to prevent elections in U.S. and Canada from complicating the deal's passage. Pelosi, however, has been noncommittal about bringing the legislation up for a vote.