Donald Trump is warning his Pennsylvania supporters about potential voter fraud in the state and suggests that they volunteer to monitor the election.

Speaking at a Friday evening rally in Altoona, Trump says, “We don’t want to see people voting five times, folks,” and adds: “We have to be very careful.”

In 2014, a Pennsylvania judge struck down a law requiring voters to produce state-approved photo ID in order to vote.

Trump has repeatedly questioned the integrity of the nation’s voting system, an unprecedented assertion by a modern presidential candidate.

(AP)