The travel industry in the United States is on edge after Homeland Security Secretary Markwayne Mullin reiterated his threat to withdraw US Customs and Border Protection officers from airports in so-called “sanctuary cities” in a move that could jeopardize international flights.

The US Travel Association said that Mullin confirmed he is considering withdrawing CPB officers in a meeting where the trade group was pressing its concerns about other proposals the Trump administration is considering that could hamper travel.

US Travel and the major airlines quickly condemned the idea, and even Transportation Secretary Sean Duffy said it doesn’t make sense to him.