Despite staunch bipartisan opposition to US President Donald Trump’s threatened tariffs on all imports from Mexico, there are not enough votes to legislate the policy away, a top Republican senator said on Wednesday.

Senator Ron Johnson, who has been critical of the Trump administration’s approach to trade policy, said there were not enough votes to override a presidential veto. He also said he had relayed the message to Mexican officials.

“I talked to the Mexican ambassador, I wanted to make sure that she realized that if the president decides to invoke tariffs, I don’t think there’s a possibility for a veto override,” Johnson told reporters, according to The Hill.

Trump threatened to slap a 5% tariff on all Mexican goods imported to the United States, effective Monday. He issued the threat without warning on Thursday via Twitter, against the advice of cabinet members, including his top trade official. According to a White House statement, the tariff rate will go up to 25% by October unless Mexico takes drastic measures to reduce the flow of migrants across the border into the United States.

The basis for the tariffs, the White House said, was a 1977 law that authorizes the president to regulate commerce in response to an “unusual and extraordinary threat.” Using the statute to address long-standing concerns about illegal immigration is unprecedented and has stoked concerns beyond the trade relationship with Mexico.

Not only does the trade action threaten to derail the renegotiated North American Free Trade Agreement, it signals to other countries, including China, that no trade agreement will prevent the Trump administration from imposing new tariffs.

Vice-President Mike Pence met with a delegation of senior Mexican officials on Wednesday as they tried to avert the tariff escalation.

Trump said of the meeting during a press briefing in Ireland: “I think they want to make a deal and they sent their top people to try to do it. We’ll see what happens today.”