House Democrats today increased their criticism of Speaker John Boehner (R-Ohio) for hiring attorneys to defend the Defense of Marriage Act in court, alleging the legal team lacks credibility in its arguments and demanding that Members be briefed on its proceedings.

A letter written by Reps. Jerrold Nadler (N.Y.), Barney Frank (Mass.), Tammy Baldwin (Wis.), Jared Polis (Colo.), David Cicilline (R.I.) and John Conyers (Mich.) is just the latest salvo from House Democrats regarding DOMA, the 1996 law that directs the federal government to recognize marriage only between a man and a woman and allows states to refuse to recognize same-sex marriages from other states.

Democrats blasted GOP leaders for pushing to defend the law in court after President Barack Obama declared it unconstitutional in March. As a result, the Justice Department has declined to argue in favor of it.

In its latest letter to Boehner, the group charges that attorneys hired by Boehner to defend the law “have filed pleadings containing arguments and assertions that are troubling.”

For example, the letter asserts that researcher Lisa Diamond complained that lawyers hired by Boehner distorted her research on sexual identity. The lawyers cited an observation from Diamond’s study, which said half of respondents “had changed their identity label more than once since first relinquishing their heterosexual identity.” Diamond, in an affidavit, said the lawyers’ presentation of her study “misconstrues my research findings, which do not support the propositions for which [the House Bipartisan Legal Advisory Group] cites them.”

Diamond contends she was talking about the labels people identify with, not their actual sexual orientation, and she takes issue with the lawyers arguing that her research shows gays and lesbians can change their sexual preferences.

“The United States House of Representatives should not be making harmful and unreasonable arguments that demean its credibility, and that of the American people,” the Democratic lawmakers wrote. “It has been fifteen years since the Congress enacted DOMA, and the materials and arguments that [the attorneys are] making on behalf of the House do not withstand the test of time or scrutiny.”

The group further charges that “the American people, should be given the opportunity to understand why House Republican Leadership continues to advance arguments that have no valid basis and are demeaning to many of our fellow Americans.”

Boehner spokesman Michael Steel shrugged off the letter, saying in a statement, “Following the Department of Justice decision to stop defending a law passed by strong bipartisan majorities in Congress, the Bipartisan Legal Advisory Group voted to retain counsel to defend the law.”

BLAG, a group composed of the top three House GOP leaders and top two Democratic leaders, voted along party lines in March to defend DOMA in court. House Democrats quickly blasted Boehner for retaining former Solicitor General Paul Clement as the lead attorney to defend DOMA in pending court cases, charging he was not properly vetted and that the move was a waste of taxpayer dollars. Republicans, meanwhile, have maintained that Obama’s announcement instructing the Justice Department not to defend DOMA in court was a political stunt and a distraction from fiscal issues.