The White House on Friday banned the use of all government aircraft for congressional delegations without approval from the White House chief of staff during the partial government shutdown.

In a letter to the heads of all federal agencies and departments, acting Office of Management and Budget Director Russ Vought told officials that Trump asked him to explain these temporary policies regarding “legislative branch travel.”

“Under no circumstances during a government shutdown will any government owned, rented, leased or chartered aircraft support any congressional delegation, without the express written approval of the White House chief of staff,” Vought wrote. “Nor will any funds appropriated to the Executive Branch be used for any congressional delegation travel expenses, without his express written approval.”

The formal notice came a day after Trump called off a trip to Afghanistan and Brussels for House Speaker Nancy Pelosi, D-Calif., and other lawmakers.

Trump notified Pelosi the trip was canceled, which he did by revoking her access to military aircraft, just as lawmakers were departing the Capitol.

The White House said Trump wants to ensure Pelosi is in the country for future negotiations on a deal to reopen the federal government, parts of which have been shut down since Dec. 22.

Trump’s move was viewed as an escalation in his battle with Pelosi over funding for a wall along the southern border. Trump wants Congress to include $5.7 billion for the barrier in legislation to end the government shutdown, but Pelosi is opposed to his demand.

[Related: Pelosi's office cries foul after trip canceled, says Trump visited Iraq during the shutdown]