Gay rights advocates asked California's highest court Friday to keep off the November ballot a citizens' initiative that would again ban same-sex marriage.

Lawyers for Equality California filed a petition arguing that the proposed amendment to the California Constitution should be invalidated because its impact was not made clear to the millions of voters who signed petitions to qualify the measure before the state Supreme Court legalized same-sex unions.

"This court has recognized that gay and lesbian couples have a fundamental right to marry and, as of June 16, such couples have been getting married across the state," the petition states.

"Rather than effecting 'no change' in existing California law, the proposed initiative would dramatically change existing law by taking that fundamental right away and inscribing discrimination based on a suspect classification into our state Constitution."

The petition also claims the so-called California Marriage Protection Act should be disqualified because it would revise, rather than amend, the state Constitution by altering its fundamental guarantee of equality for all — in essence writing a law the state high court has already found unconstitutional into the constitution.