Mexico’s President Enrique Pena Nieto cancelled on Thursday a scheduled meeting with US President Donald Trump next week amid a deepening dispute over a border wall promised by America’s new leader.

“This morning we informed the White House that I will not attend the work meeting planned for next Tuesday with the POTUS,” Pena Nieto said on Twitter, referring to Trump. “Mexico reiterates its willingness to work with the United States to reach accords that favour both nations.”

The Mexican president’s rejection came after Trump said it was “better to cancel” the scheduled visit to Washington if Mexico was unwilling to foot the bill for a border wall.

There was much debate over who would pay for the costly wall.

Trump said throughout his campaign that he would force Mexico to pay, a proposal Mexico has repeatedly rejected.

The White House said on Thursday that Trump wants a new 20 percent tax on imports from Mexico to pay for the barrier on the southern border.

Trump wants the measure to be part of a broader tax overhaul package that the US Congress is contemplating, White House spokesman Sean Spicer told reporters.

Explaining how the tax would work, Spicer said: “We have a new tax at $50 billion at 20 percent of imports -which is, by the way, a practice that 160 other countries do right now.”

“Our country’s policy is to tax exports and let imports flow freely in, which is ridiculous. But by doing it that way we can do $10 billion a year and easily pay for the wall. Just through that mechanism alone,” Spicer said.

No further details were available.

Manuel Suarez-Mier, a columnist for Mexico’s Excelsior newspaper, told Al Jazeera from Washington, DC that Trump’s ultimatum came as a surprise for the Mexican government.

“The minister of foreign affairs and the minister of commerce were in Washington from Mexico on Wednesday and Thursday to determine the details for the upcoming meeting of the presidents on Tuesday. And Trump comes out and announces that the wall will be built and Mexico will have to pay for it,” said Suarez-Mier.