The city attorney ruled that Councilman Fred L. Barrera cannot list the title mayor pro tem as his occupation on the November ballot for the mayoral election.
The move came after Councilwoman Joanne Coontz, Barrera's opponent in the mayor's race, had an attorney file a protest with the city clerk.
Barrera said he will challenge the ruling.
California's Elections Code states that candidates may only use the title of elective office won by a "vote of the people," City Atty. Robert Franks wrote in a Wednesday memo to the city clerk. Barrera was elected to his role of mayor pro tem by the City Council.
Barrera said he has hired an attorney to prepare a lawsuit to challenge Franks' decision.
"The ruling has exceptions, and precedent has been set," Barrera said. Both Gene Beyer and Don Smith used the title on ballots when they ran for mayor, he noted.
Barrera's campaign spokesman, David Hart, said his candidate has a strong claim to the title since Mayor Beyer has been almost consistently absent from council meetings because of ill health.
Franks said the city's legal staff had discussed those issues but had decided that the wording of the code was clear. Some 1991 amendments clarified the statute and would override the precedents Barrera cited, he said.