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DENVER (KDVR) — Election primary politics are getting more heated. A U.S. Senate flyer appears to break federal election law.

The flyer features Senate candidates Ron Hanks and Joe O’Dea. The flyer does not say who paid for the ad, which is against the law.

It also says “Colorado Republican Party” endorses Hanks. Officially, the party is known as the “Colorado GOP” and has a strict policy of not endorsing any candidate and has not endorsed Hanks.

His opponent, O’Dea, is suing to stop the flyers, saying they could sway the outcome of the Senate primary.

“These repeated campaign violations by unknown, dark-money actors have the express purpose of meddling in Colorado’s Republican primary to deliberately misinform voters days before Election Day,” his campaign said in a news release. “Urgent action is necessary to prevent these unknown actors from sending additional false mailers that do not contain disclosures required by law and do not identify who is responsible for their contents.”

The Colorado GOP called the mailers “criminal and false.”

“Let me be clear: the Colorado GOP has not and does not endorse in primary races. These verifiably false and malicious mailers are criminal and we will be taking action,” Colorado GOP Chairwoman Kristi Burton Brown said in a statement.