PORTLAND, Ore (Reuters) - Oregon Democratic Congressman David Wu, accused of an unwanted sexual encounter with a campaign donor's teenage daughter, said on Tuesday he will resign his seat to defend himself against "these very serious allegations."
The decision by Wu, 56, to step down came a day after he announced he would not seek an eighth term in office, as Nancy Pelosi, the top-ranking Democrat in the U.S. House of Representatives, referred the matter to the House Ethics Committee for investigation.
Wu becomes the latest in a long line of politicians from both parties to become caught up in sex scandals over the years, and the second House Democrat in little over a month to have his tenure cut short by such a controversy.
New York Representative Anthony Weiner resigned in June after he admitted lying about sending lewd photos of himself to women over the Internet.
Wu's conduct has been called into question previously. He acknowledged earlier this year he was undergoing psychiatric treatment after his staff complained of erratic behavior, including his e-mailing of a picture of himself dressed in a tiger costume.
Wu, the first Chinese-American elected to Congress, did not give a precise date for his resignation, saying only that he planned to step down "effective upon the resolution of the debt-ceiling crisis."
Congress faces an early August deadline to pass legislation raising the nation's debt ceiling to avoid a U.S. default on its obligations.
While he made no explicit mention of the exact misconduct he is accused of, Wu said in his statement, "I cannot care for my family the way I wish while serving in Congress and fighting these very serious allegations."
Wu represents Oregon's heavily Democratic 1st Congressional District, which encompasses the western side of Portland, the state's largest city, as well as more rural areas in Oregon's northwestern corner.
The governor will call for a special election to fill Wu's seat for the remainder of his term.
Two other Democrats already had declared their intention to challenge Wu in next year's primary before the scandal broke -- state labor commissioner Brad Avakian and state lawmaker Brad Witt of Clatskanie, Oregon, northwest of Portland.
No Republicans have immediately announced plans to run. But Oregon Republican Party Chairman Allen Alley called the 1st District "absolutely a winnable Republican seat," citing what he described as a shift in the national political tone.
Although Democrats account for 42.4 percent of registered voters in the district, compared with 30.1 percent for Republicans, a sizable bloc, 27.5 percent, are registered as members of various third parties or are unaffiliated.
In 2010, Wu's Republican challenger, Rob Cornilles, lost by 10 percentage points.
Alley said several Republicans were considering a bid for Wu's seat in the special election.
The latest allegations against Wu surfaced last week when the Portland Oregonian newspaper reported the daughter of a high school friend who contributed to Wu's campaign accused him of making an unwanted sexual advance around Thanksgiving of last year.
Details of the nature of the alleged encounter have not been disclosed. Wu has not denied the accusation but has acknowledged more than once the allegation was "serious."
"I have absolutely no desire to bring unwanted publicity, attention or stress to a young woman and her family," he said in a statement issued over the weekend.
The Oregonian said Wu's accuser, who has not been identified, was from Orange County, California, graduated from high school in 2010, and was 18 at the time of the alleged incident.
The newspaper said several of Wu's staff listened earlier this year to a distraught voice mail left by the woman, accusing Wu of aggressive and unwanted sexual advances.