The House Ethics Committee wrote a letter to California Republican Rep. Duncan Hunter on Thursday notifying him that his guilty plea to campaign finance violations means that, under House rules, he may not vote on the House floor.

House Rule XXIII, Clause 10(a) bars members "convicted by a court of record for the commission of a crime for which a sentence of two or more years’ imprisonment" from "participation in the business of each committee of which such individual is a member, and a Member should refrain from voting on any question at a meeting of the House or of the Committee of the Whole House on the state of the Union."

The ban is lifted if "judicial or executive proceedings result[s] in reinstatement of the presumption of the innocence of such Member" or if the "Member is reelected to the House after the date of such conviction."

READ THE ETHICS COMMITTEE'S LETTER

The Ethics committee said the rule “was promulgated to preserve public confidence in the legislative process.” The panel noted that if Hunter violates the rule, “you risk subjecting yourself to action by this Committee, and by the House, in addition to any other disciplinary action that may be initiated in connection with your criminal conviction.”

Hunter did not vote on Thursday during the four roll call tallies taken on the House floor. He has already indicated he's on his way out of office, in a break for California's beleaguered GOP that increases the chances of the party keeping one of its few remaining House seats in the heavily Democratic state.

In this July 1, 2019, file photo, U.S. Rep. Duncan D. Hunter, R-Calif., leaves federal court after a hearing in San Diego. Hunter has indicated he's on his way out of office. (AP Photo/Denis Poroy, File)

But Hunter's pending departure also comes with a measure of uncertainty. There is no clear Republican favorite to succeed him in the San Diego County district, setting the stage for several months of party infighting in a race that could turn on local political loyalties or the potential involvement of President Trump.

After months of professing his innocence, the 42-year-old Hunter pleaded guilty Tuesday to a single charge of conspiring with his wife to illegally use at least $150,000 in campaign funds for personal expenses. Among the improper spending were a birthday gathering for his young daughter at a posh hotel and a social outing with friends at a French bistro in Washington.

In announcing his plan to plead guilty, the former combat Marine talked about the need for a smooth transition in his district but didn't say when he will depart Congress, leaving unclear whether or not a special election will be scheduled to fill the vacancy.

Hunter is scheduled to be sentenced on March 17, two weeks after California's primary election.

Holding the 50th Congressional District, which has an 11-point Republican registration edge, will be critical if the party hopes to reclaim control of the House after losing it to Democrats in 2018.

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Hunter had been actively running for reelection while under indictment. After his guilty plea, San Diego County Republican Chairman Tony Krvaric said the party “is not worried about losing this seat.”

The field of GOP contenders who earlier lined up to challenge Hunter includes Carl DeMaio, a former San Diego city councilman who now is a local political commentator and radio host; former Congressman Darrell Issa, who built a national reputation when he headed the House Oversight and Government Reform Committee and was a foil to President Barack Obama; and state Sen. Brian Jones, who highlights that he's the only major Republican candidate who lives in the district east of San Diego.

California Republican Rep. Duncan Hunter, center right, walks out of federal court Tuesday, Dec. 3, 2019, in San Diego. Hunter gave up his year-long fight against federal corruption charges and pleaded guilty Tuesday to misusing his campaign funds, paving the way for the six-term Republican to step down. (AP Photo/Gregory Bull)

Democrat Ammar Campa-Najjar, a 30-year-old former Obama administration official who nearly defeated Hunter in 2018 after the congressman was indicted, is widely expected to be one of two candidates who emerges from the March primary for a November showdown.

Under California election rules, the top two vote-getters in the primary advance to the general election, regardless of party affiliation.

Part of the challenge for candidates will be introducing themselves to voters who have seen the Hunter name on the ballot for decades. Hunter has held the seat for 11 years after being elected to succeed his father, Duncan L. Hunter, who was in office nearly three decades before him.

"This is Trump country," said Thad Kousser, a political science professor at the University of California, San Diego. “The conventional wisdom is that only an indicted or convicted Duncan Hunter could lose this seat for Republicans, and now he won't have that chance.”

Kousser said Campa-Najjar's job has become tougher with Hunter's pending exit, noting that the Democrat exceeded expectations in 2018 and showed himself a skilled campaigner and fundraiser.

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"It's too early to count him out," Kousser said.

Campa-Najjar said voters in the district don’t want “coastal elites and career politicians,” a reference to his GOP rivals. “I think it’s time we have a congressman who has integrity.”

Fox News' Chad Pergram and Andrew O'Reilly contributed to this report, as well as The Associated Press.