"I have real problems with ballots being sent," Trump said during a rally in Greeley. "Like people say, 'Oh, here's a ballot. Here's another ballot, throw it away. Oh, here's one I like, we'll keep that one.'"
Trump acknowledged that most people believe Colorado's voting system is "legitimate" but, he said, "Perhaps I'm a more skeptical person."
"You can go to University Center and they'll give you a ballot, a new ballot – they'll void your old ballet," Trump claimed. "You can go out and make sure it gets in. Now, in some places they probably do that four or five times, but we won't do that."
It's unclear where Trump's assertion came from. The Colorado Secretary of State's Office told KDVR that people can't submit a second ballot if they already submitted the one mailed to them.
This year is Colorado's first mail-in presidential election, according to The Denver Post. The state first started doing mail-in elections in 2014.
Trump's call for multiple votes came days after one of his supporters was arrested in Iowa and accused of voter fraud. Terri Lynn Rote is accused of turning ballots in at two different polling places because she is convinced the election is rigged.
The claim has been repeated multiple times by Trump, who wrote in an Oct. 17 tweet that, "Of course there is large scale voter fraud happening on and before election day."
There is no evidence of widespread voter fraud in the United States, according to PolitiFact.