SAN FRANCISCO—The California Supreme Court refused to hear a challenge July 16 to a vote that could ban same-sex marriages in the state.

The unanimous decision means that, barring further legal action, voters will consider a constitutional amendment in November that would again limit marriage in California to a union between a man and a woman. The court did not give a reason for deciding not to accept the case.

If it passes, the amendment, known as Proposition 8, would overrule the California Supreme Court decision that legalized same-sex marriage in the state as of June 16.

Equality California and other gay rights groups issued a statement saying they were confident that the initiative, similar to gay marriage bans enacted in 26 other U.S. states, would fail.

“We’re disappointed, but this ruling does not affect the campaign against Prop. 8 in any way,” the groups said. “We have been focused on continuing the election and moving forward.”

Equality California filed a petition last month arguing that the signature petitions used to put the proposal on the ballot, printed up before the court struck down the state’s marriage laws, were misleading because they stated that the initiative would have no legal or financial effect.

The gay rights group also claimed that Proposition 8 would so drastically alter the promise of equality written into the California Constitution that it was improper to put it before voters as an amendment.