President Joe Biden is expected to sign an executive order on immigration as early as this week, according to sources familiar with the decision.

The long-awaited executive order would limit the number of migrants that would be allowed to claim asylum at the southern U.S. border. It would immediately send them back to Mexico to wait until the daily average goes down and, once it goes down, they would be able to claim asylum. The exact number that would trigger a pause on claiming asylum is still under deliberations, the sources said.

In recent days, members of Congress have been briefed on the executive action, according to sources familiar with the briefings.

Any executive order, administration officials caution, would be challenged in court.

“I anticipate that if the president would take executive action, and whatever that executive action would entail, it will be challenged in the court,” Homeland Security Secretary Alejandro Mayorkas told reporters last month at Department of Homeland Security headquarters.

Mayorkas and other members of the administration have urged Congress to pass the bipartisan border bill that was negotiated and proposed earlier this year.

This is a developing story. Please check back for updates.