President Donald Trump said he’ll close the southern border next week unless Mexico “immediately” stops illegal migration into the U.S.

Trump has periodically threatened to close the border, where he’s declared a national emergency because of the number of migrants crossing illegally. It’s unclear what he means, since closing the border entirely would halt millions of dollars worth of cross-border commerce. Trade with Mexico totaled $616 billion in 2017, according to the office of the U.S. Trade Representative.

Apprehensions of undocumented immigrants spiked in February to more than 76,000, compared to 58,295 the month before, according to U.S. Customs and Border Protection.

Most congressional Democrats and some Republicans disagree that there’s an emergency. Congress passed a resolution earlier this month disapproving of Trump’s plan to divert money from the Pentagon to construction of a border wall. Trump vetoed the resolution and Democrats couldn’t muster the votes to override him.

-By Alex Wayne, Bloomberg News