Senate Republicans are considering taking legislative action against President Donald Trump’s planned new tariffs on Mexico, laying the foundation for potentially explosive infighting between the president and his party, reported The Washington Post, Politico and Bloomberg.

Trump has threatened to impose a 5% tariff on Mexican goods on June 10 if Mexico doesn’t do more to stop the massive flow of migrants crossing its northern border into the U.S.

The president would need to declare a national emergency at the border to impose the tariffs, but Congress has the authority to pass a resolution of disapproval that would overrule such a declaration.

Congress voted to block Trump’s first national emergency declaration to fund his border wall in March, but the president swiftly vetoed it.

Trump, during a joint press conference Tuesday with British Prime Minister Theresa May, said it would be “foolish” for Republicans to block the tariffs.

“I think it’s most likely that the tariffs go on,” Trump said during the London press conference, adding that he doesn’t believe GOP lawmakers will vote to override him. “I think if they do, it’s foolish.”