The House Ethics Committee formally announced Friday that it is launching an investigation into Rep. Laura Richardson, the embattled California Democrat who faces allegations that she forced her congressional staff to work on and make contributions to her re-election campaign.

Rep. Laura Richardson (D-Ca.)

In a statement Friday, the ethics panel said that its members had voted unanimously on Thursday to establish a special subcommittee to investigate Richardson, who has already been investigated – and cleared – once before by the ethics committee since first winning election to the House in a 2007 special election.

Richardson said in a statement that she “look(s) forward to a full, fair and expeditious inquiry” and that she is “confident that once the Subcommittee is able to gather all the facts, and we are permitted to respond, they will conclude positively.”

She also blasted the ethics panel for what she described as “unjustly” targeting certain members based on their race and gender and accused the committee of engaging in “discriminatory conduct in pursuing two investigations against me while simultaneously failing to apply the same standards to or take the same actions against other Members -- of whom the overwhelming majority are white males.

“Specifically, numerous Members have used their House offices for personal lodging, in some cases for years, saving tens of thousands of dollars personally at taxpayers’ expense,” Richardson said. “Under House rules, personal use of House resources is as impermissible as political use. Accordingly, I will raise this issue with the Ethics Committee.”

Richardson is African American.

News of the investigation comes five months after the organization Citizens for Responsibility and Ethics in Washington called on the FBI to conduct a criminal investigation into Richardson after obtaining documents that the watchdog group said showed the California Democrat had pressured her Washington staff to work on her re-election campaign. Richardson’s office has denied the allegations.

The Los Angeles Times reported Thursday that according to a source familiar with the panel’s preliminary inquiry, at least eight current and former Richardson staffers “told investigators they felt compelled to work on her 2010 re-election campaign on their own time.”

In 2009, the ethics panel investigated whether Richardson had improperly benefited when a bank canceled the sale of her foreclosed home. Richardson was unanimously cleared by the panel last year – a point she noted in her statement Friday.

“During this period, I will continue to provide representation and service to my constituents,” Richardson said. “I urge all to recall that the Committee’s step today ‘is to investigate only’ and that less than one year ago, I was completely exonerated after a similar investigation.”

Richardson also faces a tough re-election bid in 2012, with a June primary against fellow Rep. Janice Hahn (D) and state Assemblyman Isadore Hall (D). As The Post’s Aaron Blake noted last month:

Washington Democrats wouldn’t be terribly sad to see either of these incumbents lose, as Hahn under-performed in a recent special election and Richardson’s personal troubles have mounted. The good news for the establishment is that they could both lose.

With an ethics committee vote looming, Richardson had earlier this week sent a letter to the members of the secretive panel in an eleventh-hour attempt to dissuade them from moving forward with an investigation, Politico’s John Bresnahan reported.

The investigation by the four-member subcommittee is likely to take months. Serving as the panel’s chairman will be Rep. Charlie Dent (R-Pa.). Rep. John Yarmuth (D-Ky.) will be the subcommittee’s ranking member, and the other two lawmakers on the panel will be Reps. Rob Bishop (R-Utah) and Ben Ray Lujan (D-N.M.).

Rep. Linda Sanchez, like Richardson a Democrat from California, “recused herself from consideration of this matter to avoid even the appearance of a conflict of interest,” the ethics committee said in its statement Friday.

This story has been updated.