U.S. Trade Representative Robert Lighthizer sent House Democrats a new offer on the stalled United States-Mexico-Canada Agreement in an effort to resolve their concerns about the trade deal and finally put it to a vote.

House Ways and Means Chairman Richard Neal said Wednesday there has been significant progress on two of four issues that Democrats sought to change.

“I don’t think anybody is quite ready yet to show their final hand but the discussions continue to go forward,” he said. “The one that still appears stubborn is labor enforcement.” Neal didn’t give details.

Some Democrats have suggested forcing Mexican factories to improve labor conditions by putting import restrictions on their products if they fail to meet sufficient labor conditions. Republicans have called the idea unworkable.

The other changes Democrats are seeking include environmental protections, drug patent provisions and enforcement mechanisms for the overall deal.

Kevin Brady, the top Republican on the Ways and Means panel, said he hopes lawmakers and the White House will agree to provisions that would allow arbitration panels to be formed under the new agreement. Under the existing North American Free Trade Agreement, each party has the power to block such panels, meaning provisions have gone unenforced.