Republican senators staged a boycott of the nomination of Gina McCarthy as head of the Environmental Protection Agency Thursday, surprising the top Democrat on the Senate committee in charge of the vote and furthering a pattern of delay that also postponed a confirmation vote on President Barack Obama's Labor nominee Wednesday.

"I am rather stunned that this is happening," said Sen. Barbara Boxer, D-Calif., the committee chairwoman. "I never even knew they were boycotting this until I got a letter [Thursday] morning."

In a letter sent to Boxer, the Republican committee members said the EPA was "stonewalling" their requests for further information on McCarthy.

"As you know, all Republicans on our EPW committee have asked EPA to honor five very reasonable and basic requests in conjunction with the nomination of Gina McCarthy which focus on openness and transparency," they wrote. "While you have allowed EPA adequate time to fully respond before any mark-up on the nomination, EPA has stonewalled on four of the five categories. Because of this, no Republican member of the Committee will attend [Thursday]'s mark-up if it is held."

Sen. David Vitter, R-La., the committee's top Republican, said in a release that McCarthy had provided "nonresponsive answers" and left Republicans "completely unsatisfied."

The absence of all eight Republican committee members left the panel without a quorum, though had all Democrats been present, they would have been able to proceed. Boxer, however, dismissed that approach – at least for now.

"Today we are asking the Republicans to come back, we will schedule another mark-up," she said, adding it was never her intention to push the confirmation today without Republicans present.

But the Democrats present at the hearing each took their turn bashing their conservative colleagues over the walkout, extolling McCarthy's experience and willingness to answer what they called an unprecedented number of questions.

"They may not like the answers, but she's given them the answers," said Sen. Tom Carper, D-Del. "I'm an old governor, I believe that elections have consequences."

The Republicans, in an attempt to buffer themselves from criticism, cited a boycott precedence in 2003 when Democrats did the same thing to oppose an EPA nominee, Michael Leavitt, under the Bush administration.

"Leavitt was scheduled for a committee vote on Oct. 1, 2003. Due to the Democrat boycott, the Committee vote was postponed until Oct. 15, 2003," Vitter said in a release. "Leavitt received a vote on the Senate floor on Oct. 28, 2003."

Boxer said the Republicans were making "false accusations" that their questions were going unanswered and they were merely blocking McCarthy because they disagree with her and the Obama administration's position on the environment. She accused them of "harassing and haranguing" McCarthy.

"At this stage, their opposition even to allowing us to vote shows how outside the mainstream they are, it shows how obstructionist they are, it shows how their pledge to do better with women voters is false," Boxer said. "How could you have a more qualified woman than Gina McCarthy? This is outrageous. Get out of the fringe lane."

Boxer, who is currently working with Vitter to pass water resource legislation, said she would speak to her Republican counterpart on reaching an agreement for moving forward on McCarthy, who already received a unanimous Senate confirmation for her current position.