In papers submitted to the state Supreme Court, lawyers for the Protect Marriage coalition argued that Brown had "invented an entirely new theory" by asking the justices to trump the electorate, which approved Proposition 8 to amend the state Constitution to limit marriage to a man and a woman.
"We will not mince words. The attorney general is inviting this court to declare a constitutional revolution," reads the brief co-written by Kenneth Starr, dean of Pepperdine University's law school and former independent counsel who investigated President Bill Clinton.
The competing positions come in a series of legal challenges to Proposition 8 brought after the ballot initiative passed with 52 percent of the vote on Nov. 4. Brown initially said he would defend the measure in his role as attorney general.
But in a dramatic reversal, he changed course two weeks ago and joined same-sex marriage supporters in asking the court to void Proposition 8 and to uphold the estimated 18,000 same-sex unions sanctioned during the four months gay marriage was legal in the state.
Lawyers for the couples, gay rights groups and cities that brought the cases argue that the measure's backers used a flawed process for qualifying the amendment for the ballot.
Brown, however, argues that the amendment itself is unconstitutional because the Supreme Court established marriage as a fundamental right in its May decision striking down previous one man-one woman marriage statutes.
Starr and co-counsel Andrew Pugno maintained in their brief filed Monday that the attorney general is asking the court to assume powers not granted by the Constitution.
"The judiciary is entirely a creature of the Constitution, not an independent, freestanding guardian of minority rights or natural law," they wrote.
In an interview Monday, Brown responded that it was the sponsors of Proposition 8 who have misunderstood the role of the courts in a democratic society.
"Mr. Starr ignores the fundamental doctrine of judicial review and the historic duty of the Supreme Court to guard our fundamental liberties," he said.
Also Monday, lawyers for San Francisco and five other counties, as well as for gay couples who married during the four-month window, asked the court to let stand the existing marriages even if it upholds Proposition 8.
They argued that nothing in the language of Proposition 8 nor the ballot arguments submitted by Protect Marriage made it clear the gay marriage ban was designed to apply retroactively.
Proposition 8's sponsors have argued that the 14-word measure, which holds that "only marriage between a man and a woman is valid or recognized in California," effectively bars the state from acknowledging any same-sex marriages, regardless of when they were sanctioned.