The president of the United States intends to impose a 20 percent tax on imports from Mexico to cover the cost of a wall spanning the nations’ border, the White House spokesman told reporters on board Air Force One,

Donald Trump has already made up his mind about the tax, Sean Spicer said.

The tax, however, cannot be immediately levied because of the North American Free Trade Agreement (NAFTA), the more than two-decade-old accord linking the U.S., Canada and Mexico that the president has repeatedly criticized as a destroyer of American jobs.

Earlier Thursday, Trump said that he and Mexican President Enrique Peña Nieto had jointly agreed to cancel their planned Jan. 31 meeting in the U.S. because of the neighboring country’s refusal to pay for the wall.

“The president of Mexico and myself have agreed to cancel our planned meeting scheduled for next week,” Trump said in a speech during a gathering with congressional Republicans in Philadelphia.

“Unless Mexico is going to treat the United States fairly, with respect, such a meeting would be fruitless and I want to go a different route. We have no choice,” the president said.

In a series of tweets Thursday morning, Trump said Mexico should pay for a wall on the nations’ border because it had long benefited from NAFTA at Americans’ expense.

He pointed out that the US has been running trade deficits with Mexico that amount to roughly $60 billion annually and said it would be better to cancel his planned meeting with Peña Nieto if Mexico refused to reimburse its neighbor for the cost of the wall.

A border wall was one of the main campaign promises made by Trump, who launched his bid for the White House by saying that many undocumented migrants who make their way to the United States were criminals, including drug dealers and rapists.

Trump on Wednesday signed several executive orders affecting immigration, including one that assigns federal funds for the construction of the border wall.

Peña Nieto, who has repeatedly insisted that Mexico will not foot the bill for the wall and did so again on Wednesday, announced on Twitter that the meeting was off.

“We informed the White House this morning that I will not attend the meeting scheduled for Tuesday with the @POTUS,” he wrote.

Prior to Trump’s remarks in Philadelphia, Spicer said the administration would look to hold the meeting at another time and keep the lines of communication open. EFE