SAN FRANCISCO (JTA) — In November, San Franciscans will vote on a ballot measure that would outlaw circumcision on boys under the age of 18.

Although experts say it is highly unlikely the measure will pass — very few state propositions pass, much less one this controversial — the mere fact that it reached the ballot, and in such a major city, has caused much concern for Jews and their allies.

Opponents of the bill see it as a violation of the Constitution’s protection of religious rights and an infringement on physicians’ ability to practice medicine. More than that, however, the measure is being seen as a frontal attack on a central tenet of Judaism.

“The stakes are very high,” said Nathan Diament, director of the Orthodox Union’s Institute for Public Affairs. “Circumcision is a fundamental aspect of Jewish ritual practice and Jewish identity. While we certainly hope the prospect of its being enacted is remote, the precedent it would set and the message it would send would be terrible, not just in the United States but around the world.

“We don’t just want it defeated,” he said, “we want it defeated resoundly.”