A large group of Republican senators including Majority Leader Mitch McConnell (R-Ky.) wrote to President Trump on Tuesday urging him not to withdraw from the North American Free Trade Agreement.

The letter signed by 36 GOP senators was released just hours before Trump is to deliver his State of the Union address to Congress. It served notice that whatever Trump’s message is on trade, many in his party will not stand with him if he makes good on his threats to withdraw from the accord between the United States, Canada and Mexico.

The letter comes one day after the latest round of talks to renegotiate the trade pact ended in Montreal. It is carefully worded to appeal to Trump’s successes, pointing to them as a reason to stay in the trade deal.

“Mr. President, your leadership has jump-started our economy. The recent tax reform bill is already leading to economic success across all industries and the stock market is at record highs,” the senators wrote. “The next step to advance the economy requires that we keep NAFTA in place, but modernize it to better reflect our 21st century economy. We look forward to working with you and your administration to make that modernization a reality and bring Americans even greater economic success.”

The letter also notes that “a wide range of industries in the U.S. have benefited from this agreement and American consumers are reaping those benefits, too.”

Trump campaigned on promises to withdraw from NAFTA, deriding it as a terrible deal that had cost U.S. jobs and destroyed manufacturing. Despite pressure from GOP lawmakers and business leaders, he’s kept up the criticism since taking office. Earlier this month, Trump tweeted that NAFTA was a “bad joke” and vowed to use the bargaining over a trade deal to make Mexico pay for a wall along the U.S. southern border.

Trade is an issue with the potential to divide the GOP, since most congressional Republicans, especially in the Senate, support free trade and oppose the protectionist policies espoused by Trump. A number of lawmakers voiced opposition last week when the administration imposed tariffs on imported solar panels and washing machines.

Sen. Patrick J. Toomey (R-Pa.), one of the signers of Tuesday’s letter, said in an interview that “I am not aware of a single Republican senator who wishes for the United States to withdraw from NAFTA.”

Toomey said he found the tariff decision “very disturbing” and it contributed to the urgency to send a message on NAFTA.

“Among Republican senators there’s very, very strong support for staying in NAFTA. I think most of us believe there are things that can be improved upon, there are certainly things that can be updated to reflect economic and technological changes,” Toomey said. “But this has been a very, very good trade agreement for the United States and certainly Pennsylvania, and we wanted to communicate that because in part, let’s face it, the president has at times expressed a lot of skepticism about NAFTA.”

A sixth round of talks aimed at reaching a new North American trade deal ended in Montreal on Monday having made only limited progress. Trade officials agreed on a new treaty’s anti-corruption provisions and narrowed the gaps over customs issues. But on the main U.S. proposals, including a bid to restructure auto industry supply chains, they remain far apart.

Negotiators from the three countries have been meeting since August in hopes of rewriting the 24-year accord, which the president has repeatedly assailed as unfair to his working-class base.

But despite his vow that the negotiations could be used to make Mexico pay for a border wall, Mexican officials say privately that the wall has not been discussed in the talks.

U.S. Trade Representative Robert Lighthizer told reporters on Monday that the administration wants to encourage the return of manufacturing jobs to the United States and to eliminate incentives for corporations to move their operations offshore. Many economists say those jobs are gone for good.

In recent weeks, NAFTA supporters have flocked to the White House in an effort to educate the president on the downside of giving up on the deal. Republican senators and representatives of affected industries and agricultural groups have stressed that walking away could push down stock prices and lead to the loss of export jobs tied to Mexico and Canada.

Political concerns were not far from negotiators’ minds in Montreal. A congressional delegation including Rep. David G. Reichert (R-Wash.), the chairman of the House trade subcommittee, met with Lighthizer to show congressional backing for the deal.

Lighthizer is pushing negotiators to accelerate their efforts between now and the next round of talks, scheduled for late February in Mexico.