Wu's spokesman, Erik Dorey, said the seven-term Democrat had a telephone conversation on Saturday with House Democratic Leader Nancy Pelosi about the allegation, which was first reported by The Oregonian newspaper. Dorey would not comment on the substance of the conversation

An aide to Pelosi declined Saturday to comment on Wu.

The allegation seemed to be boiling into yet another sex scandal confronting a member of Congress. It comes a month after Rep. Anthony Weiner stepped down after getting caught sending suggestive pictures of himself on his Twitter account.

Late Friday, the 56-year-old Wu issued a one-sentence statement about The Oregonian's report: “This is very serious, and I have absolutely no desire to bring unwanted publicity, attention or stress to a young woman and her family.”

Pressure was building on Wu to publicly address the allegation. There were also calls for his resignation.

“I'm saddened to hear this news. David owes the citizens he represents a detailed explanation,” said State Rep. Brad Witt, who is running against Wu in the Democratic primary next spring. “If this accusation proves to be true, it's time for David Wu to resign and get the help he needs.”

Another challenger of Wu in the Democratic primary, state Labor Commissioner Brad Avakian, said Saturday Wu should resign immediately.

“I think any 56-year-old man, especially a 56-year-old Congressman, that asserts himself like this on an 18-year-old girl, has got no business serving in Congress,” Avakian said at a news conference. “There is nothing that can be explained that makes this situation right. He's got to resign.”

Former Oregon Secretary of State Bill Bradbury, also a Democrat, called on Wu to step down now.

“Obviously I think the right decision would be to resign,” Bradbury told the AP. “I felt that way (after previous reports of erratic behavior) and I feel that even more strongly now.”

Earlier this year Bradbury announced he was supporting Avakian, and at the time called Wu “damaged goods.”

Tom Chamberlain, Oregon AFL-CIO president, wouldn't speculate on Wu's chances to get the powerful labor group's nod in the 2012 election, as Wu has in past elections, but said “it's a high threshold.”

Still, Chamberlain said “it's too early” to say whether Wu should step down.

Citing anonymous sources, The Oregonian reported that Wu told senior aides that the sexual encounter last November with the young woman in California was consensual. The paper reported Facebook notes indicate she graduated from high school in 2010 and that she registered to vote in California last August.

The paper said the woman decided not to press changes because there were no witnesses and it would have been her word against Wu's.

The newspaper said its information came from multiple sources familiar with the allegation.

The Oregonian's report adds new troubles for a congressman who fought accusations of strange and erratic behavior during his re-election campaign last year. Seven members of his re-election campaign quit in January because of behavior that included sending a photo of himself in a tiger costume to a staff member and an angry public speech.