The unanimous ruling by the three-judge panel of the California Court of Appeal reversed a July 22 decision by superior court Judge Peter Busch allowing Alioto-Pier -- who has already served nearly seven years as supervisor -- to run again this November.
The city charter limits supervisors to two successive four-year terms.
Mayor Gavin Newsom appointed Alioto-Pier to replace him as District 2 supervisor in 2004 after he was elected mayor.
She then won an election in November 2004 to serve out the remaining two years of the four-year term and was re-elected to another four-year term in November 2006.
San Francisco City Attorney Dennis Herrera had argued that Alioto-Pier's first term counted as a full term, citing a "rounding-up" rule on midterm appointments enacted by voters in 1990. Alioto-Pier contended the appointed term should not count for term limits, but the appeals court ruled it did.
"Twenty years ago the voters of San Francisco imposed term limits on their supervisors, so that... a person appointed to complete more than two years 'would be deemed to have served one full term,' with his or her service rounded up," the appeals court wrote in its decision today.
The court added that nothing had changed in the past two decades to alter the two-term limit or the rounding-up rule.
"Alioto-Pier has already served two consecutive terms. She may not seek a third," the court stated.
Alioto-Pier's attorneys promised today to appeal to the California Supreme Court and to ask for an emergency review to allow time for her to make it on the ballot should the court rule in her favor.
In a prepared statement, Herrera's office said the decision "strongly vindicates" its position. Herrera had advised Alioto-Pier in 2008 that she was ineligible to seek another term.
"I am grateful to the Court of Appeal for recognizing the obvious intent of San Francisco voters, and for affirming the clear meaning of the law," Herrera said.
He added that he has "consistently defended" Alioto-Pier's right to pursue the dispute in court.
"I wish her and her family every success in their future endeavors," Herrera said.
Tom Pier, Alioto-Pier's husband, attorney and campaign spokesman, said the campaign would file a petition to the California Supreme Court on Wednesday.
"We feel that the Court of Appeal misinterpreted the plain language of the charter and issued an opinion that is contrary to existing law," Pier said.