The California Teachers Assn., one of the state's most politically powerful unions, suffered a rare rebuke Thursday when Republican state senators blocked the confirmation of a union leader to another term on the state Board of Education.

The Senate rejected Joe Nunez, the CTA's deputy executive director and a chief architect of public labor unions' successful campaign against Gov. Arnold Schwarzenegger's 2005 effort to upend Sacramento politics. Nunez was appointed to the board in 2001 by former Gov. Gray Davis, a Democrat. To the surprise of many, Schwarzenegger reappointed him last year.

To be confirmed, Nunez needed two-thirds of the Senate, but only two of 15 Republicans voted for him, which wasn't enough for a supermajority. Both of them, Abel Maldonado of Santa Maria and Jeff Denham of Salinas, had been endorsed by the union in a previous election.

"He was on the board and supposed to be independent, and he was running a campaign against the administration for his employer," said Assembly GOP leader Dick Ackerman of Irvine. "This is a conflict you can't get around."