Arizona Republican Trent Franks on Thursday announced he is resigning from Congress, facing a House Ethics Committee investigation as to whether he engaged in conduct that constitutes sexual harassment.

According to Franks' statement, the committee is reviewing an inquiry in which he discussed surrogacy with two former female subordinates, when he and his wife faced infertility.

"I have recently learned that the Ethics Committee is reviewing an inquiry regarding 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,' Franks said in his statement.

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CBS News' chief congressional correspondent Nancy Cordes reported that Franks and his wife tried to adopt and their attempts were not successful. They eventually had twins via a surrogate and they wanted to have another child. But, as Cordes reports, the statement does not make clear if he brought up the topic with staffers, making them uncomfortable, or asked them to be surrogates.

A former Franks staffer, Rebeccah Heinrichs, said on Fox News Thursday that Franks had "talked about surrogacy" in the office as he and his wife struggled with infertility and had "uncomfortable conversations." Heinrichs

"I have never been made to feel uncomfortable being with the congressman. I have never seen any slightest bit of sexual harassment or intimidation," Heinrichs said. "He has treated every single member that I've seen of his staff with dignity and respect. So this is incredibly startling to me and frankly I find it a tragedy."

His resignation will become effective Jan. 1 of 2018. Roll Call first reported that Franks was expected to resign.

According to Speaker of the House Paul Ryan's office, the counsel to the speaker was contacted by a friend with information about Franks roughly two weeks ago, and Ryan's office believed that claim warranted further investigation. After more conversations and interviews, Ryan brought the information to Franks, and a complaint was filed with the House Ethics Committee. Franks eventually decided to offer his letter of resignation.

According to a House Ethics Committee statement dated Thursday, the committee had established an investigative subcommittee "to determine whether Representative Trent Franks engaged in conduct that constitutes sexual harassment and/or retaliation for opposing sexual harassment, in violation of House rules, laws, regulations, or other standards of conduct."

"It is with the greatest sadness, that for the sake of the causes I deeply love, I must now step back from the battle I have spent over three decades fighting," Franks' statement said later. "I hope my resignation will remain distinct from the great gains we have made. My time in Congress serving my constituents, America and the Constitution is and will remain one of God's greatest gift to me in life."

Franks, an eight-term Republican, considers himself a conservative in the mold of former President Ronald Reagan. In Congress, he established himself as one of the most vocally pro-life members. He serves on the House Armed Services Committee and Judiciary Committee. He's also a member of the conservative Republican Study Committee.

Franks had also been mulling a run for Sen. Jeff Flake's seat in 2018 after Flake announced he would not seek re-election.

His resignation comes on the same day that Sen. Al Franken announced he would soon resign from the Senate, after the majority of his Democratic colleagues in the Senate urged him to step aside. Multiple women accused Franken of inappropriately touching them or attempting to kiss them.

CBS News' Catherine Reynolds contributed to this report.