Sean Parker, a Silicon Valley celebrity for serving as Facebook’s (FB) first president and a cofounder of Napster, is backing an initiative to legalize marijuana in the state, CNN Money reports. The billionaire plans to put millions behind the ballot initiative, according to the L.A. Times.

“It’s very encouraging to see a vibrant community of activists … coming together around a sensible reform-based measure that protects children, gives law enforcement additional resources and establishes a strong regulatory framework for responsible adult use of marijuana—one that will yield economic benefits for all Californians,” he said in a statement to the Times.

The measure would legalize marijuana for all adults over the age of 21 and place a limit of six plants on personal cultivation. Growers would pay taxes, and the measure proposes a sales tax of 15%.

California currently allows medical marijuana use, but the last attempt to legalize marijuana broadly was shot down by voters in 2010. This time around, the measure already has the support of Calif. Lt. Governor Gavin Newsom, who said it would “strengthen law enforcement, respect local preferences, protect public health and public safety, and restore the environment.”