Congressional Republicans, worried about the possible economic fallout from President Donald Trump’s plan to impose a tariff on Mexico, have discussed taking legislative action to head off his plan, a person familiar with the matter said on Monday night.

GOP lawmakers are considering whether to revive a resolution of disapproval over the national emergency declaration that underpins Trump’s justification for the tariffs, according to the person, who asked not to be identified to discuss sensitive deliberations. The action would also stop the president from spending billions on a border wall without congressional approval.

Congress earlier this year passed a similar resolution, but the House didn’t have enough votes to override a presidential veto.

The political calculation for Republicans considering a resolution to rebuke their own president could be different this time, as they fear the economic impact of a 5% tariff on all imports from Mexico starting on June 10 unless that country’s government curbs illegal migration to the U.S. The tariff could rise to as high as 25% by October unless Mexico takes sufficient action, as judged by the Trump administration.

The discussions occurred as top GOP Senators warned the administration that Congress could reclaim its tariff powers or hold up a new North American free trade deal if the White House carries out its threat to impose the levies. It would take a critical mass of congressional Republicans publicly supporting this legislative rebellion to convince Trump to reverse course before the tariffs are set to being next week.

Senate Finance Chairman Chuck Grassley, an Iowa Republican, suggested he won’t begin consideration of the U.S.-Mexico-Canada free trade agreement if the Mexico tariffs are put in place. Grassley used a similar threat to convince the White House to drop tariffs on steel and aluminum from Mexico and Canada earlier this year.

“It’s the same trouble that we had with the aluminum and steel tariffs. They have to come off before we can take it up here” he said of the USMCA.

Trade Authority

The No. 2 Senate Republican, John Thune of South Dakota, said Congress could eventually act to curb emergency presidential trade powers if Trump carries out his threat to increase tariffs to 25% by October.

“I suspect Congress is going to want to be heard from, for sure,” Thune said. “We have a lot of our members who don’t like where this is headed, about what it means for the economy generally and don’t see it as a path to solve immigration issues.”

Senators Mitch McConnell and John Thune
(in the center) Senators Mitch McConnell and John Thune

The reactions from members of Trump’s own party show just how far he has pushed his fellow Republicans who have traditionally supported free trade. The disagreement within the GOP is not just ideological—there could be a political price to pay as well, especially in states where much of the economy depends on trade with neighboring countries.

Senator Mike Rounds, also from South Dakota, said that his state’s corn farmers are poised to feel the brunt of any Mexican retaliation.

“I think it is very fair to say that Congress should take a look at the authority they have sent to the executive branch, regardless of who the president is,” Rounds said. He added that South Dakotans want Trump to succeed but may need supplemental assistance if they are on the “tip of the spear” in fighting illegal immigration from Mexico.

Texas Senator John Cornyn said that any legislation curbing Trump’s powers would be difficult given his veto power.

“The challenges legislatively on this are obvious,” Cornyn said. “The president of the United States is going to have a say, so the best way forward is dialogue.”

Iowa Senator Joni Ernst said that Congress may act but senators “need to sort through the legalities” of the authorities granted to each branch of government according to the Constitution and current law.

Only a few Republicans have expressed any level of support for Trump’s move against Mexico, and frustration with the new tariffs was evident throughout the Republican caucus on Monday.

Senate Agriculture Chairman Pat Roberts of Kansas called them “extremely counterproductive” and Colorado Senator Cory Gardner said they are “a bad idea, plain and simple.”

Republican senators have asked the administration for a briefing on the strategy. One specific concern is what Mexico must do to avoid the tariffs taking effect and scaling up.

“I just hope they can reach some kind of agreement to delay this and continue to talk,” Thune said. “The market doesn’t like uncertainty and these kind of things create uncertainty, which is why you have seen the kind of volatility in the markets.