Republican Sen. John Ensign said money paid to his mistress was in fact a result of their affair.
Ensign's parents gave $96,000 to the family of his former mistress, Cindy Hampton.
The 51-year-old conservative Christian said the money was given "out of concern for the well being of longtime family friends during a difficult time."
"None of the gifts came from campaign or official funds, nor were they related to any campaign or official duties," Ensign's attorney, Paul Coggins, said in a statement.
But one Washington watchdog group is suspicious and calling on the Justice Department to investigate.
"When you have an affair with someone in your office, who is married to someone else in your office, and then you fire them both and then on top of it you have your rich parents come in and pay them off, I think it's hard to imagine a situation that is more embarrassing," said Melanie Sloan executive director of Citizens for Responsibility and Ethics in Washington.
Mrs. Hampton and her husband previously worked for Ensign. The two families were close friends for decades.
Sen. Ensign denied the payments were hush money.