Rubio said the possibility highlighted the need for congressional action because the alternative would be legalization without benefits like border security and an E-Verify system to require employers to check their workers' legal status.
"We can't leave it… the way it is because I think a year from now we could find ourselves with all 11 million people here legally under an executive order from the president, but no E-Verify, no more border security, no more border agents," Rubio said.
The White House disputed Rubio's comments. Asked whether Obama would be "tempted" to issue executive orders as Rubio suggested, White House spokesman Bobby Whithorne said, "No. The only solution to this problem is for Congress to fix the broken immigration system by passing comprehensive reform."
Rubio's comments came with lawmakers back home in their districts for a five-week summer recess, which activists on both sides of the immigration issue are trying to use to make their case for or against action in the GOP-controlled House.
Under pressure from advocates for reform, several House Republicans have already indicated qualified support for a path to citizenship for the immigrants already here illegally, something that's part of the Senate bill but opposed by many conservatives.
But it remains unclear whether one side will clearly prevail when lawmakers return to Washington in September. GOP House leaders have said they plan to proceed with the immigration reform with single-issue bills, beginning with border security, so it remains to be seen whether they'll get to the point of entering negotiations with the Senate on a package that could reach Obama's desk.
Rubio's comments Tuesday tracked with speculation from immigration activists on the left about how to move forward if Congress never sends Obama a bill. The possibility of pressuring Obama to take additional executive actions has been discussed, though most advocates with ties to the White House say it's premature to focus on that idea.