Sen. Marco Rubio (R-Fla.) is feeling the heat as potential GOP allies are now turning against his immigration reform bill.

Republican colleagues who were previously viewed as possible “yes” votes are keeping their distance from the 1,075-page measure.

On Wednesday, conservative activists ripped Rubio and Sen. John McCain (R-Ariz.) — both sponsors of the bipartisan immigration measure — at a Capitol Hill rally.

The crowd, which was protesting the bill’s effort to put millions of illegal immigrants on a path to citizenship, booed at the mention of Rubio’s name during the six-hour event.