US and Mexican trade negotiators have reached a deal making changes to labor enforcement under a new continent-wide trade agreement, Fox Business reported Monday.

That could remove a principal hurdle to ratification of the US-Mexico-Canada Agreement, the fate of which has seemed to hang by a thread in recent weeks.

Top Mexican officials were due to address the media later Monday.

Citing unnamed sources, Fox Business said a final deal could emerge in the next 24 hours that would allow all three countries to ratify the modified treaty.

A senior Democratic aide in Congress told AFP officials on Capitol Hill were still studying the proposal.

"No agreement to announce yet," the person said on condition of anonymity.

With the window narrowing for action by the Democrat-controlled House of Representatives, as 2019 draws to a close and an election year approaches, there has been a flurry of last-minute activity on the trade pact in recent days.

Jesus Seade, Mexico's top trade negotiator, arrives at the Office of the US Trade Representative in November  2019
Jesus Seade, Mexico's top trade negotiator, arrives at the Office of the US Trade Representative in November 2019 AFP / SAUL LOEB

CNBC reported that congressional Democrats and the administration of President Donald Trump were "near a tentative deal" and that a vote could he held by December 18.

Lawmakers also face competing priorities as they press ahead with impeachment proceedings and legislation to prevent a government shutdown this month.

More than a year ago, the United States, Mexico and Canada signed an update to the North American Free Trade Agreement, changing rules on auto and digital trade, Mexican labor laws, intellectual property and dispute settlement systems for investors.

Mexican lawmakers ratified the deal in June but Democrats in Washington and US labor leaders have raised concerns -- looking for stronger guarantees that new Mexican labor laws will be enforced to prevent unfair competition with US workers.

US House Speaker Nancy Pelosi in recent weeks has sent positive signals, saying an agreement was imminent.

Mexican President Andres Manuel Lopez Obrador said last week he would not accept a US proposal for supervisors to oversee the implementation of Mexico's labor reforms under the USMCA.

Mexican Foreign Minister Marcel Ebrard said Sunday his country would not accept immediate application of minimum requirements for metal content in automobiles.