Donald Trump slammed Sen. Ted Cruz Monday over a controversial piece of campaign mail that was made to look like a "voting violation" notice for Iowa voters.

"The Cruz [mailer] is unbelievable," Trump said Monday during an appearance on MSNBC's "Morning Joe." "It looks right out of municipal government."

Trump, who leads Cruz by just a few points in the latest polls heading into Monday's Iowa caucus, called the direct mail campaign a "total fraud" and suggested Cruz is being investigated for the effort to get his supporters to vote with the notice.

"It's absolutely amazing," Trump said. "It's a disgrace."

Trump expressed confidence that he would prevail over his chief rival in Iowa, but stopped short of agreeing that Cruz could be "finished" if he loses in the Hawkeye State caucus Monday.

"He's put everything he can into Iowa," Trump said. "He's doing terribly in New Hampshire."