"Harvey Milk does not rise to the level of a special day of recognition," said Mettler at Monday night's board meeting.
Milk fought for gay rights and was the first openly gay man to hold an elected office in California. Gov. Arnold Schwarzenegger signed Harvey Milk Day into law Oct. 12 last year.
Milk was elected to the San Francisco Board of Supervisors and was assassinated in November 1978.
Several speakers at the board meeting strongly disagreed with Mettler's proposal, saying Milk was more than just a gay politician.
"He gave kids hope," said Centennial High School senior Tyler Lozano. "That's something that a lot of lesbian and gay kids don't have in my school."
Mettler is also running for public office in the 32nd Assembly District Republican primary. Mettler denies he brought up the anti-Milk proposal as a way to shore up his conservative credentials.
"Not at all, I believe in this," said Mettler.
The school board will vote on Mettler's proposal at a May 19 meeting.
Mettler also brought up another proposal. He called for a resolution supporting a state bill that would honor Ronald Reagan. That passed on a 4-1 vote.