Democratic challenger Kay Hagan has filed a defamation lawsuit against Sen. Elizabeth Dole (R-N.C.) for questioning Hagan's faith in what is shaping up as the nastiest campaign of this cycle.

Hagan announced the lawsuit after Dole refused to remove the ad, which suggests Hagan is an atheist and has become the subject of tough criticism from several newspaper editorials in North Carolina. Several polls show Dole trailing Hagan, a state senator.

In the ad, Hagan, a Presbyterian who taught Sunday school, called Dole’s ad “offensive” and closed with a dig that suggests Dole broke one of the Ten Commandments.

“Elizabeth Dole's attacks on my Christian faith are offensive,” Hagan says, adding her campaign is about jobs and the economy instead of "bearing false witness against fellow Christians."

The Ninth Commandment prohibits bearing false witness against a neighbor.

Dole spokesman Daniel McLagan dismissed Hagan’s response as “fairly hysterical.” He noted that everything in Dole’s ad is true.

“It's sad that she has stooped that kind of name-calling,” he said.

Hagan’s campaign filed the lawsuit to ensure Dole could not “slander” Hagan without consequences, spokeswoman Colleen Flanagan said in a statement.

“Elizabeth Dole would love nothing more than to distract from the issues and her record for the last five days of the campaign,” Flanagan said. “In filing this suit, we’ve made clear that these kind of despicable tactics will not be tolerated, and our campaign is moving forward with the most important task at hand: defeating Elizabeth Dole, and giving North Carolina’s families a voice in the U.S. Senate that they’ve been sorely missing.”

Dole’s ad, released Tuesday afternoon, highlights a Hagan fundraiser hosted by an adviser to the Godless Americans political action committee. The political spot shows that the Godless Americans support removing the words "In God We Trust" from money and the phrase "under God" from the Pledge of Allegiance.

It ends with a picture of Hagan and an unidentified female voice saying, “There is no God!”

Hagan said the Dole campaign faked her voice to make voters think that she doesn’t believe in God.

“Well, I believe in God,” Hagan says in her own advertisement. “I taught Sunday school. My faith guides my life, and Sen. Dole knows it.”

Hagan's campaign has noted that her family has attended the same Presbyterian church for more than a century.

Dole’s ad has also come under scrutiny from local newspapers. The Charlotte Observer wrote in an editorial Thursday that it was the “modern-day version” of Sen. Jesse Helms’s (R-N.C.) “white hands” ad, which critics have condemned as a ploy to drum up racist fears about his 1990 Democratic opponent. The Greensboro News & Record wrote that Dole’s ad is “worse than dishonest” and called on her to pull it from the air.

Hagan is leading Dole 46.6 percent to 42.9 percent in the latest Pollster.com trend line of all polls taken of their Senate race.

Ian Swanson contributed to this story.