A group that has led the fight against tax increases in California endorsed Arnold Schwarzenegger (search) for governor Thursday, providing a big boost to the actor's candidacy by vouching for his hostility to tax hikes.

The Howard Jarvis Taxpayer's Association (search) faxed its endorsement to Schwarzenegger's campaign early Thursday. Fox News obtained a copy of the letter, which the Schwarzenegger campaign is due to release later in the day.

"While we have great respect for others involved in this race, you are uniquely qualified to bring a positive, pro-taxpayer message to millions of Californians who may have never heard it before," Jarvis Association President Jon Coupal wrote to Schwarzenegger. "Moreover, your personal commitment to Proposition 13 has been unequivocal."

The Jarvis group was the driving force behind Proposition 13, the 1978 citizen's initiative that cut California property taxes by 30 percent and mandated an annual increase of no more than 2 percent in subsequent years.

"The reason is really quite simple," Coupal told Fox News in a phone interview. "There probably is no candidate that articulates as strongly a pro-taxpayer position."

Schwarzenegger's GOP rival and state Sen. Tom McClintock (search) has a long history with the Jarvis group and has steadfastly identified himself as the only reliably pro-taxpayer candidate running on the replacement ballot in the Oct. 7 recall election.

The Jarvis endorsement undercuts that line of attack against Schwarzenegger and may pave the way for other groups opposed to tax increases to back the international film star. Coupal said Schwarzenegger is both pro-taxpayer and electable. Since McClintock's hostility to tax increases has never been questioned, Coupal was implying McClintock will be less electable on Oct. 7.

Coupal said his group withheld its endorsement until Schwarzenegger laid to rest lingering concerns about his support for Proposition 13. Schwarzenegger's chief economic adviser, billionaire Democrat Warren Buffett (search), told the Wall Street Journal earlier this month California's property taxes were too low and hinted they might have to be raised.

Schwarzenegger rebuffed Buffett in a written statement soon after. At his first press conference, with Buffett sitting immediately to his left, the actor turned to the investment wizard and said: "I told Warren, if he mentions Proposition 13 one more time, he has to do 400 push ups."