The California Supreme Court on Tuesday upheld a ban on same-sex marriage in the state while ruling that the unions of roughly 18,000 same-sex couples who were wed last year will remain valid.

The court's ruling upheld the constitutionality of Proposition 8, the voter-approved measure that banned same-sex marriage.

Voters approved Proposition 8 in November. The ban sparked outrage from gay rights advocates and prompted mass protests across the state.

In the days after the passage of Proposition 8, three lawsuits were filed directly with the state Supreme Court challenging the validity of the measure.

The state's highest court heard oral arguments in March from attorneys supporting the measure and from those representing plaintiffs who claim the measure is unconstitutional and improperly amended the state constitution.

A host of organizations filed petitions with the court in support of the challenges. The city and county of Los Angeles both joined a lawsuit filed by the city and county of San Francisco challenging the measure.

In Tuesday's 6-1 ruling, the court determined that the proposition legally adjusted the state's constitution.

"Having been approved by a majority of the voters at the November 4, 2008 election, the initiative measure lawfully amends the California Constitution to include the new provision ...," according to the court's decision.

"In a sense, petitioners' and the Attorney General's complain is that it is just too easy to amend the California Constitution through the initiative process," the justices concluded.

"But it is not a proper function of this court to curtail that process; we are constitutionally bound to uphold it. If the process for amending the constitution is to be restricted -- perhaps in the manner it was explicitly limited in an earlier version of our state constitution ... or as limited in the present-day constitutions of some of our sister states ... this is an effort that the people themselves may undertake through the process of amending their constitution in order to impose further limitations upon their own power of initiative."

On the question of whether the marriages of same-sex couples who wed last year should be allowed to stand, the court ruled that Proposition 8 cannot be used to invalidate them.

"Applying well-established legal principles pertinent to the question whether a constitutional provision should be interpreted to apply prospectively or retroactively, we conclude that the new section cannot properly be interpreted to apply retroactively," according to the ruling.

"Accordingly, the marriages of same-sex couples performed prior to the effective date of Proposition 8 remain valid and must continue to be recognized in this state," the ruling said.

(Xinhua News Agency May 27, 2009)