Florida Republican Sen. Marco Rubio warned Tuesday that if Congress doesn’t pass immigration overhaul legislation, President Barack Obama may act on his own to legalize the 11 million immigrants already in the U.S. illegally.

Rubio, a potential presidential candidate and an author of the sweeping immigration bill that passed the Senate in June but stalled in the House, noted that the Obama administration took action a year ago to give legal status to many immigrants brought here illegally as children. He said without congressional action, the president might well be tempted to do the same for everyone else here illegally, too.