Arizona Republican Trent Franks has resigned amid an ethics investigation into claims he repeatedly asked female staff to be surrogate mothers.
The announcement came after a congressional panel said it was opening an inquiry into sexual harassment allegations against Mr Franks.
The lawmaker acknowledged discussing surrogacy with two female aides when he and his wife were facing infertility.
He is the third member of Congress to resign in three days.
The Associated Press reports one of Mr Franks’ former aides accuses him of offering her $5m (£3.7m) to act as a surrogate mother, repeatedly pressing her to carry his child.
She told the news agency that another female staff member had also been approached by Mr Franks about surrogacy.
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One of the aides reportedly said Mr Franks retaliated against her after she turned down his alleged surrogacy requests by ignoring her and withholding assignments.
A spokesman for the eight-term congressman – who has a net worth of $33m – would not comment on whether he had offered aides money to act as surrogates.
Mr Franks said on Thursday his resignation would take effect next month.
But on Friday he said he had decided to quit immediately after his wife was admitted to a Washington hospital “due to an ongoing ailment”.
In a statement on Thursday, the 60-year-old Republican acknowledged “my discussion of surrogacy with two previous female subordinates, making each feel uncomfortable.
“I deeply regret that my discussion of this option and process in the workplace caused distress.”
Mr Franks said he and his wife, Josephine, had used a surrogate to carry their two twins.
He stood down as the House of Representatives ethics committee opened an inquiry against him into a matter that “constitutes sexual harassment and/or retaliation for opposing sexual harassment”.
Republican Speaker of the House Paul Ryan said he had advised the congressman to stand down.
The ethics committee also announced on Thursday it was investigating Texas Republican Blake Farenthold amid claims of sexual misconduct against him by a former member of staff.
It was revealed last week that Mr Farenthold used $84,000 of taxpayer money to settle a sexual harassment lawsuit with his former communications director.
The resignations of two Democratic lawmakers have already shaken Washington this week.
Democratic congressman John Conyers announced on Tuesday that he will step down after multiple aides accused him of sexual misconduct.
Hours before Mr Franks’ announcement, Minnesota Democratic Senator Al Franken said he too was resigning over claims of groping after several Democrats called on him to step down.
