The Trump administration could have a new fight on its hands if it tries to rush a NAFTA deal through Congress this spring.

Two Democrats who sit on the influential trade sub-committee are urging negotiators to focus on getting a good deal rather than a quick deal.

"The worst mistakes are made when you let time determine substance," said Michigan Congressman Sander Levin during an interview with CBC News from his office on Capitol Hill.

"The public ... they're not interested in timelines. They're interested in what an agreement means in their lives."

Congressman Ron Kind, a fellow Democrat from Wisconsin, agrees that the U.S. should not make compromises for the sake of meeting a deadline.

"A bad negotiated agreement is gonna be hard to pass Congress," Kind told CBC News. "If they need more time to get it right, they gotta take the time. Otherwise the agreement is going to be a tough lift."

Getting a deal is just the beginning

The pleas highlight the complicated process ahead if Canada, the United States and Mexico are finally able to reach agreement on an updated NAFTA.

Legislators in each country must approve any new deal before it can be implemented.

In the U.S., NAFTA is a deeply divisive issue both for Democrats and Republicans — which makes it all the more likely that a fast deal could be a tough sell.

Democratic Congressman Ron Kind represents Wisconsin's third congressional district. "They gotta take the time. Otherwise the agreement is going to be a tough lift." (CBC)

"Canada is very aware of the essential role that Congress plays in any trade agreements in the United States," said Foreign Affairs Minister Chrystia Freeland during a news conference Thursday.

"That's why throughout the process we have been speaking a lot with both senators and congressmen and women. It has been an ongoing dialogue."

The pleas for caution come as a week of high-level NAFTA negotiations wrap up today in Washington.

Freeland has met multiple times in recent days with her American counterpart, U.S. Trade Representative Robert Lighthizer, and Mexico's Secretary of the Economy Ildefonso Guarjardo.

She also spent much of Thursday on Capitol Hill, where she held additional meetings with Republican House Speaker Paul Ryan and Kevin Brady, chair of the House Ways and Means Committee.

A source with direct knowledge told CBC News that both Ryan and Brady emphasized the urgent need to get an agreement by May 17 in order to give the current session of Congress enough time to approve a deal.

The source said May 17 is a "real deadline" and that negotiators would have a 30-day period to work out further details.

Momentum around the negotiating table appeared to slow down this week, as the U.S. and Mexico continued to disagree about changes to the auto sector.

Putting the pressure on Mexico

The Americans are pushing Mexico to increase labour and wage standards, while demanding changes that could boost vehicle production in higher-wage countries, like the U.S., and Canada. Mexico presented a series of counter-proposals which were not well received by the Americans.

Levin said he supports the U.S. push for Mexican concessions.

"Mexico needs to address the suppression of workers and keeping wages low ... as a matter of governmental policy as a basis for luring industry from the U.S. and Canada," Levin said.

Unless such changes are included in the deal, he said, it won't get his backing.

"We've made that very clear from the very beginning."

Kind said there has been a "deplorable lack of communication" from the Trump administration about what is happening with the negotiations.

"I have been trying to set up meetings with Bob Lighthizer and others of the Trump team for many weeks now, just to try to sit down and exchange views and make sure that he is hearing from members of Congress who will ultimately have a vote in this."