AFL-CIO President Richard Trumka warned Congress Monday against scheduling a vote on President Trump's U.S.-Mexico-Canada Agreement on trade without significant changes.

He said, however, that he believed the deal, which would replace the 1993 North American Free Trade Agreement, could still be salvaged.

"This deal is incomplete. A vote would be premature. To move forward with the ‘New #NAFTA’ in its current form would be a colossal waste of an important opportunity. However, there’s still time to fix this deal," Trumka tweeted Monday.

He added: "The administration can win our support. But, it’s going to take a lot more work. It cant be rushed to fit a campaign schedule. It’s too important for that. #NAFTA."

The White House has been lobbying Congress hard to take up USMCA and hopes to secure congressional approval by this summer. Congressional leaders, however, have not committed to any timeline for votes.

The AFL-CIO has expressed qualified support for the deal, which includes provisions that require 75 percent of a car be made in the U.S., Canada, or Mexico in order for it to be duty-free, up from 62.5 percent, and for at least 40 percent of its parts to be made by workers earning $16 an hour. The deal also requires to Mexico to reform its labor laws to allow unions to be more independent and free from government regulation.

However the labor federation said last month that Mexico had to "fully and effectively implement [the] reforms to its labor law" before it would endorse the U.S. Congress taking up the deal.

"We believe the changes to Mexican labor law must be enacted and implemented. Mexico must show us they have the enforcement mechanism otherwise the changes are useless," Trumka tweeted Monday. "Any efforts to push the ‘New #NAFTA’ through in its current form will be met with nationwide opposition."

Mexico's ambassador to the U.S., Martha Barcena, said at a D.C. forum on USMCA in February that her country was "very and totally committed to amend the labor laws," and that the current administration was just "waiting for the debate to take place" in Mexico's legislature, the Congress of the Union. However, the legislature has moved slowly on the issue, leaving White House officials to wait for news.

The AFL-CIO also criticized the deal for preserving patent protections for drugmakers and lacking an effective monitoring system for its rules.

[Related: Robert Lighthizer woos Democrats on USMCA]