WASHINGTON (AP) — President Donald Trump said Tuesday he wants to use the military to secure the U.S.-Mexico border until his promised border wall is built.

Speaking during a visit with Baltic leaders, Trump said he’s been discussing the idea with his Defense Secretary, Jim Mattis.

“We’re going to be doing things militarily. Until we can have a wall and proper security, we’re going to be guarding our border with the military,” he said, calling the measure a “big step” that had rarely been done before.

Federal law prohibits the use of active duty service members for law enforcement inside the U.S., unless specifically authorized by Congress.