A just-filed ethics complaint is reigniting a long-running debate about whether one of Washington, D.C.’s most prominent watchdog groups is impartial or tilts to the left.

The complaint is widening a rift between Citizens for Responsibility and Ethics in Washington and House Oversight and Government Reform Chairman Darrell Issa (R-Calif.).

The conflict is unusual because government watchdog groups and top oversight officials typically have a symbiotic, even cooperative, relationship.

Issa, however, has charged that CREW raises significantly more ethics questions about Republicans than Democrats. The complaint has a long history, and there is even a website devoted to proving it, with statistics detailing which party CREW targets.

But in past years, CREW has also faced complaints from the left, such as for investigating an Education Department regulation. In February, the Democracy Alliance, a group of wealthy Democratic benefactors, left CREW off a list of recommended funding priorities, urging its members donate to what are, broadly speaking, more partisan groups.

The current flap began July 11, when CREW asked the Justice Department and an independent ethics office to examine whether Issa broke any laws or House rules when he disclosed the contents of a sealed wiretap application in the Congressional Record.

As first reported by Roll Call, during floor debate on whether to hold Attorney General Eric Holder in contempt of Congress for his alleged knowledge of a controversial “gun walking” program on the U.S.-Mexico border, Issa entered into the record a letter to Rep. Elijah Cummings (D-Md.) that quotes from and describes a wiretap application that has become central in the oversight committee’s probe of the “Fast and Furious” operation.

The wiretap applications are important because they were reviewed and approved by senior Justice Department officials and contain detailed descriptions of the controversial tactics at the heart of the Fast and Furious scandal.

Instead of focusing on the substance of the letter, CREW asked whether Issa had broken any laws or standards in disclosing its contents to the public.

“Although the Speech or Debate Clause of the Constitution may shield Rep. Issa from prosecution for placing the contents of the sealed wiretap application into the Congressional Record, it would not prevent prosecuting him for discussing the sealed matter with reporters or taking steps to ensure the dissemination of the wiretap application to reporters for publication,” CREW Executive Director Melanie Sloan wrote to Holder.

The request put a group devoted to transparency in the unusual position of defending the government for withholding documents and attacking a lawmaker for disclosing them.

In response, Issa’s office alleged bias, calling it “shameful” that the group would make itself “complicit” in a “cover-up.”

Issa’s hometown newspaper, U-T San Diego, sided with him in an editorial, calling CREW a “Dem defender” that was “abetting an Obama administration cover-up.”

In an interview, Sloan dismissed the criticisms and pointed to recent instances in which she has raised ethics questions about Democrats.

Sen. Dean Heller (R-Nev.) “has been running an ad saying we’re an independent watchdog group because of our criticisms of [Democratic Rep.] Shelley Berkley. And I think we have been all over the New Jersey papers about [Democratic Rep.] Rob Andrews. So it’s just ridiculous,” she said.

Issa spokesman Frederick Hill said that while CREW does target Democrats, it only does so when the evidence against them is considerable.

“It’s like in the movie ‘The Departed’ when the character Colin Sullivan figures out Frank Costello was an FBI informant and Costello says, ‘I never gave up anybody who wasn’t going down anyway,’” Hill said.

CREW has gone after some high-profile Democrats, including in 2006, when Rep. Nancy Pelosi, set to become Speaker, sought the late Rep. John Murtha (D-Pa.) as her Majority Leader.

Sloan ripped the move in the press, and some of her liberal donors fled. The episode, she told Roll Call, culled from its donor base those who were afraid of rough-and-tumble ethics conflicts that hurt Democrats.

Still, critics of the group have, over the years, assembled evidence that overall, CREW targets more Republicans than Democrats.

Last year, Berman and Co., a public relations firm that CREW investigated and made the subject of a website called “Berman Exposed,” turned the tables and created a website titled “CREW exposed.”

The site includes a photograph of six months’ worth of CREW’s press releases, lawsuits, reports and other materials. The 3.5-inch stack of documents targeting Republicans is far more voluminous than the 1/8-inch stack of documents about Democratic-related complaints.

Sloan cut her political teeth working for Congressional Democrats. But she said 10 years at CREW has “made me far more of an independent” and cited New York Mayor Michael Bloomberg as someone whose political stances she identifies with.

CREW was originally founded by Norman Eisen, the U.S. ambassador to the Czech Republic, who formerly served as President Barack Obama’s internal ethics cop. Eisen told Ms. magazine in 2007 he launched CREW to provide a balance to Judicial Watch and other right-wing legal watchdogs.