Updated: 1:13 p.m.

Top Senate Republicans huddled in Minority Leader Mitch McConnell’s (R-Ky.) office Tuesday as the news that veteran Republican Sen. Arlen Specter (Pa.) was bolting the GOP for the Democratic Party.

Virtually all Members in attendance, including National Republican Senatorial Committee Chairman John Cornyn (Texas), said they didn’t know of the decision and sought to characterize the news as “rumor— until they had a chance to discuss the matter. Specter, who is up for re-election in 2010 and was facing a tough challenge from the right, is expected to hold a press conference later this afternoon.

Specter confirmed his plans in a statement. Despite the switch, Specter made clear that he would not be a guaranteed vote for Democrats and would not vote for the pro-labor Employee Free Choice Act. He earlier said he wouldn’t support moving forward on the controversial issue this year.