Key Democrats said Wednesday that they still opposed moving forward on President Trump's U.S.-Mexico-Canada Agreement on trade until some further changes are made. They said that despite the White House, Canada, and Mexico addressing several Democratic demands.

Sen. Ron Wyden, D-Ore., the ranking Democrat on the Senate Finance Committee, said in a letter to U.S. Trade Representative Robert Lighthizer that he still had serious concerns about USMCA's mechanisms for resolving investor-state disputes. "I have been open to hearing arguments as to how it may actually work. So far, the Administration’s justification for this mechanism has only increased my worry that the new Agreement will not be enforced," he said.

Wyden also reiterated concerns often expressed by Democrats regarding whether Mexico will live up to its obligations under the trade deal to reform its labor laws. Resolving the dispute settlement problem could resolve this issue as well, he said by "shoring up the ability to bring labor cases under dispute settlement."

Rep. Earl Blumenauer, D-Ore., who chairs the Ways and Means Committee's trade subcommittee, raised similar objections during a hearing Wednesday. He said labor enforcement under the 1993 North America Free Trade Agreement was extremely poor and therefore must be addressed in the USMCA, which is intended to to replace NAFTA.

"In every case in which a labor complaint has been filed [under NAFTA], there remain ongoing and serious concerns regarding compliance with the labor obligations. In the only case in which the United States has pursued dispute settlement — the Guatemala labor case — it took nearly a decade to receive a final ruling, and the United States lost the dispute," Blumenauer noted.

Rep. Bill Pascrell, D-N.J., said enforcement of trade deals is central to their effectiveness: "Without it, an agreement isn't worth the paper it is printed on. Period. We know that we cannot continue with a broken dispute settlement process that lingers like a fog from the first NAFTA. Congress cannot and will not be fooled by false promises."

The Trump administration, Canada, and Mexico have been trying in recent weeks to resolve issues lawmakers have raised regarding USMCA. On Friday, the White House exempted Canada and Mexico from tariffs on steel and aluminum. Canada and Mexico responded in Monday by removing retaliatory the tariffs that they had enacted last year. Many lawmakers had balked at holding a vote on USMCA until the tariffs, which they argued were doing more harm than good to the U.S. economy, had been lifted.

Mexico also amended its labor laws last month to bring them in line with what Democrats have demanded as part of the USMCA deal.

USMCA's backers had hoped the changes would build momentum towards the Democrat-led House holding a vote. But the Democratic leaders have balked at holding one anytime soon.