A conservative group filed a complaint Thursday with the Senate Ethics Committee, alleging Democratic Sen. Bill Nelsonbroke the law this month when claiming Russian operatives had penetrated Florida’s election apparatus.

Florida officials have insisted they are aware of no such cyber strike by foreign actors, and last week the Department of Homeland Security and the FBI said they had no evidence that such an attack has occurred. Mr. Nelson made the remarks while speaking with reporters in Tallahassee on Aug. 7 shortly before early voting began in Florida, saying he had been told Russian agents had already “penetrated” the Sunshine State’s electoral equipment and now had “free rein to move about.”

“The Senate Select Committee on Ethics should investigate Senator Nelson to determine whether he disclosed classified information or made false statements with the inherent authority of the Senate for political purposes,” wrote Kendra Arnold, the executive director of the Foundation for Accountability and Civic Trust. “In either instance, Nelson committed a serious violation and must be held accountable.”

The letter was addressed to the Ethics Committee chairman, Georgia Republican Sen. Johnny Isakson, and the committee’s co-chair, Delaware Democratic Sen. Chris Coons.