Democrat Kay Hagan responded by issuing a cease-and-desist letter and charging Dole with slander, The Hill reported.
In the ad, Dole said the Godless Americans Political Action Committee held a "secret fundraiser" for Hagan. The spot shows Hagan standing beyond a partially closed door at the event, and then shows members of the group on cable news.
"Godless Americans and Kay Hagan," the announcer says. "She hid from cameras. Took Godless money. What did Hagan promise in return?"
Hagan, a member of a Presbyterian church and former Sunday school teacher, said she does not share the atheist group's views.
"I don't know what things were like when she grew up in North Carolina, but the North Carolina I was raised in would never condone this kind of personal slander," Hagan said. "I can't begin to tell you how upset I am that she has attacked my Christian faith."
The cease-and-desist order calls on the Dole campaign to pull the ad within 24 hours.