In the ad, Susan Kateley, executive director of the California Solar Energy Industries Association, said the measure mandates that renewable energy be bought from the largest providers of such resources.

"That's why most renewable producers and environmental groups oppose Prop. 7," she says in the ad, which began airing over the weekend.

That's followed in the commercial by Teresa Casazza of the California Taxpayers' Association, who said the measures allows a 10 percent hike in utility rates that consumers would pay.

In a press release announcing the ad, Casazza said the measure's language is so poorly written that it will result in lawsuits and additional costs for ratepayers.

Proposition 7, which is mostly opposed by large utilities, would mandate that utilities get half of their energy from renewable resources by 2025.

Though it has provisions to limit the effect on ratepayer utility bills to 3 percent increases, an independent analysis found no mechanism within the proposition to enforce the provision.

The measure was added to the ballot by Peter Sperling, a wealthy activist who has previously been involved in environmental causes. The measure is also opposed by both labor and business groups and both the Republican and Democratic parties.