Republican Sen. Norm Coleman has filed a defamation lawsuit against Al Franken, the Democrat seeking to unseat him in Minnesota, claiming that Franken’s TV ads falsely brand Coleman as the fourth most corrupt senator in Washington.

“Mr. Franken has chosen to push the lines of believability far beyond the bounds of truth,” said Mark Drake, communications director for Coleman’s campaign.

“That is his right, but it is not his right to break Minnesota campaign law, and we believe that is what Mr. Franken and his campaign have done.”

In addition to the corruption claim, Drake takes issue with Franken’s statement that Coleman lives “almost rent-free” in a Washington apartment, The Hill newspaper reported.

Citizens for Responsibility and Ethics in Washington earlier this year published a list of the 20 “most corrupt” members of Congress. Coleman was not on the list. But he was one of four members who received a “dishonorable mention” by the group, which Drake claims has a “cozy” relationship with Franken’s campaign, according to The Hill.

As for the “rent-free” charge, Coleman allegedly receives a discounted rate for renting a basement in political telemarketer Jeff Larson’s Washington home.

The Franken campaign said the lawsuit was a political stunt.

“Our ads are factual and true, even if Norm Coleman doesn’t like being held accountable for his conduct,” said Franken spokeswoman Colleen Murray.

The latest NBC News poll, released Thursday, showed Coleman leading Franken by six percentage points.