(Reuters) - The Missouri General Assembly will convene a special session on May 18 to consider impeachment or any other discipline that a special House investigative panel may recommend against Governor Eric Greitens, legislative leaders announced on Thursday.

FILE PHOTO: Missouri Governor Eric Greitens appears in a police booking photo in St. Louis, Missouri, U.S., February 22, 2018. St. Louis Metropolitan Police Dept./Handout via REUTERS/File Picture

The unprecedented move by the Republican-controlled legislature against Greitens, a first-term Republican governor, comes as he faces felony charges of invasion of privacy and computer tampering in separate criminal cases brought against him by prosecutors in St. Louis.

The stage for the special session was set after a petition signed by at least three-fourths of the members of the state House of Representatives and the state Senate was presented to the Missouri secretary of state for certification, House Speaker Todd Richardson said.

The petition was signed by 138 House members and 29 senators, comprising more than 80 percent of both bodies, Richardson told a news conference at the state capital in Jefferson City.

Richardson said he expects the special House investigative committee, formed in February to examine misconduct allegations against the governor, to complete its work and present a final report to the Assembly during a special session that would begin May 18 and run for 30 days.

The House and Senate are expected to complete their action on the panel’s findings within that same time frame, he added.

The petition process allowing the General Assembly to call itself into action when deemed necessary was established under a state constitutional amendment adopted by Missouri voters in 1988 and invoked for the first time this week, Richardson said.

“The call of this historic act is for the sole purpose to consider the findings and recommendation of the House committee, including disciplinary actions against Governor Greitens,” Richardson said.

Missouri Attorney General Josh Hawley, among others, has said that findings presented in the House committee’s initial report on April 11, detailing allegations of sexual coercion and physical abuse by Greitens, were grounds for impeachment. [L1N1RO26K]

A second report issued on Wednesday concluded Greitens lied to the state ethics commission last year about how a donor list from a military veterans charity he founded in 2007 and ran for several years was obtained for use by his gubernatorial campaign. [L1N1S90LI]

The Missouri state constitution counts “moral turpitude” as a impeachable conduct.

Greitens, a former U.S. Navy Seal commando and onetime rising star in the Republican Party, has come under mounting pressure from Missouri politicians of both parties to resign since becoming embroiled in a sex scandal stemming from an admitted extramarital affair with a hairdresser.

He has since come under renewed fire over questions raised by his use of the donor list to his former charity, The Mission Continues, when he was running for governor.

Greitens has called the allegations in both instances part of a smear campaign orchestrated by his political opponents. He denies any criminal wrongdoing and has vowed to remain in office while he fights to clear his name in court.

There was no immediate word from the governor or his legal team in response to Thursday’s announcement, and Richardson said he had not spoken with Greitens during the day.

Greitens was indicted in February on a single count of criminal invasion of privacy for allegedly taking a compromising photo without the consent of the woman with whom he was involved and threatening to blackmail her with it. Jury selection for a trial in that case is set to begin on May 10.

Last month, prosecutors brought an unrelated charge of computer tampering against the governor, alleging he obtained and transmitted the donor list without the charity’s consent for his own political gain.

The charges in both cases are felonies punishable by up to four years in prison.

Under Missouri law, any articles of impeachment would be proposed to the General Assembly by the special House committee.

If the full House voted in favor of impeachment, the Senate would choose a special seven-judge panel to hear the charges presented by a House case manager and then vote whether to remove the governor from office.

No Missouri governor has ever been impeached.