At least six electors — members of the Electoral College whose votes elect the President — have vowed to cast their ballots in an attempt to block Donald Trump from winning an Electoral College majority, Politico reported Tuesday. The presidential electors are mostly former Bernie Sanders supporters who hail from Washington state and Colorado.

If the electors turn out to be "faithless electors," their votes could narrow Trump's margin-of-victory in the Electoral College over Hillary Clinton. The voting is scheduled to be held when the Electoral College meets Dec. 19, according to Politico.

One elector, Michael Baca, said in a statement he wouldn’t vote for Trump.

“The Founding Fathers created the Electoral College as the last line of defense, and I think we must do all that we can to ensure that we have a Reasonable Republican candidate who shares our American values,” he reportedly said.

Another elector involved in the anti-Trump campaign, not identified by Politico, said "the controversy and the uncertainty that would immediately blow up into a political firestorm in the U.S. would cause enough people — my hope is — to look at the whole concept of the Electoral College."

Earlier this month, fans of Clinton urged voters of the Electoral College to go rogue and vote for Clinton over Trump in a Change.org petition. The petition, named “Electoral College: Make Hillary Clinton President on Dec. 19,” has crossed over 4.5 million signatures.

“Mr. Trump is unfit to serve. His scapegoating of so many Americans, and his impulsivity, bullying, lying, admitted history of sexual assault, and utter lack of experience make him a danger to the Republic,” part of the petition reads. “Secretary Clinton WON THE POPULAR VOTE and should be President.”