President Biden on Wednesday shielded thousands of Palestinians in the United States from deportation for the next 18 months, using an obscure immigration authority as he faces mounting criticism over U.S. support for Israel in the Gaza war.

About 6,000 Palestinians are eligible for the reprieve under a program called Deferred Enforced Departure, which allows immigrants whose homelands are in crisis to remain in the United States and work legally.

In a memo obtained by The New York Times, Mr. Biden said that “many civilians remain in danger” in Gaza after the Oct. 7 attacks by Hamas.

“Therefore, I am directing the deferral of removal of certain Palestinians who are present in the United States,” he said.

The decision comes as Mr. Biden faces pressure over the war, particularly among Arab Americans who were once a reliable constituency for him. In recent weeks, pro-Palestinian groups have been demonstrating outside his campaign stops, chanting “Genocide Joe.”

While Mr. Biden’s criticism of the war has grown more forceful since the Oct. 7 attack, the United States has not signaled that it plans major policy changes such as putting conditions on billions of dollars in military aid to Israel.