In a one-line order, the Supreme Court, without comment, denied a request to immediately block county clerks from issuing marriage licenses to gay and lesbian couples.
The court will now consider ProtectMarriage.com's broader legal argument that Proposition 8 should remain in force in California, considered a longshot by most legal experts.
Proposition 8 backers last week asked the state Supreme Court to intervene, arguing the U.S. Supreme Court's decision in June did not end the legal battle over California's 2008 voter-approved gay marriage ban.
In June, the U.S. Supreme Court found the ballot measure's sponsors did not have a legal right to defend the law in place of the governor and attorney general, both of whom consider it unconstitutional. As a result, the case reverted to a federal judge's 2010 ruling striking down Proposition 8 because it violated the equal protection rights of same-sex couples.