Senate Majority Leader Bill Dix quit after video of the tryst was posted on liberal blog Iowa Starting Line.
"I think Iowans hold their elected officials to a high standard". Iowa Starting Line did not name the woman but says she is a "lobbyist for various municipality groups".
Dix is a third-generation farmer who was born and raised in Iowa.
That website said the video came from an anonymous person who saw the two in a bar and recognized Sen. Dix.
Senate President Jack Whitver said he believed Dix "made the right decision" to step down after the video surfaced online.
The incident shown on the video allegedly happened March 1 at the Waveland Tap bar in Des Moines, according to Starting Line. "We don't need this ongoing story about where Senate Republican leadership is on these issues dealing with women".
Katie Ervin Carlson, an attorney in Iowa who handles sexual harassment and employee rights lawsuits, told the website prior to Dix's resignation that the sexual harassment training given to legislators and staffers after the settlement was awarded to the former GOP staffer last September apparently didn't work. The ex-employee filed a lawsuit several years ago claiming she was sacked after reporting misconduct in the workplace that included the use of sexual language. A jury past year found in her favor, and the state agreed to pay out $1.75 million in exchange for it not appealing the verdict.
Dix has maintained the ex-staffer was sacked for poor performance.
Anderson was sacked hours after filing a sexual harassment report.
According to information on iowasenaterepublicans.com, Dix has been in the Iowa Legislature since 1996 when he was elected to the Iowa House of Representatives. Some called for Dix's resignation over the Senate's treatment of the case, which was settled for $1.75 million and resulted in the creation of a human resources manager position to handle harassment complaints down the road. He became majority leader after GOP lawmakers took control of the chamber following the 2016 election.
Gov. Kim Reynolds, meanwhile, told reporters during her weekly news conference before Dix resigned that she planned to discuss the matter with Dix on Monday.
The Associated Press contributed to this article.