I just received a press release via email, which begins:

The American Civil Liberties Union, Lambda Legal and the National Center for Lesbian Rights filed a writ petition before the California Supreme Court today urging the court to invalidate Proposition 8 if it passes. The petition charges that Proposition 8 is invalid because the initiative process was improperly used in an attempt to undo the constitution’s core commitment to equality for everyone by eliminating a fundamental right from just one group– lesbian and gay Californians. Proposition 8 also improperly attempts to prevent the courts from exercising their essential constitutional role of protecting the equal protection rights of minorities. According to the California Constitution, such radical changes to the organizing principles of state government cannot be made by simple majority vote through the initiative process, but instead must, at a minimum, go through the state legislature first.
The California Constitution itself sets out two ways to alter the document that sets the most basic rules about how state government works. Through the initiative process, voters can make relatively small changes to the constitution. But any measure that would change the underlying principles of the constitution must first be approved by the legislature before being submitted to the voters. That didn’t happen with Proposition 8, and that’s why it’s invalid.