Federal agents raid Oaksterdam University this morning

A spokeswoman with the Internal Revenue Service said the raid is part of a joint investigation with the Drug Enforcement Agency but she declined to elaborate.

"It's an ongoing investigation and everything is under seal, so we're not able to comment," she said.

Oakland in many ways has served as the cradle of California's medical cannabis movement and Oaksterdam University owner Richard Lee has been at the forefront. He runs a school, a plant nursery and a dispensary, and spearheaded California's recent unsuccessful ballot initiative to legalize marijuana.

The raid comes as federal officials are stepping up a crackdown on medical cannabis dispensaries and the landlords who provide them space in which to operate.

Despite the 1996 California law that legalized marijuana for medicinal use, the feds have maintained that the dispensaries still violate federal law. They have focused on large dispensaries and others that they assert are too close to parks or schools.

Still, city officials here have expressed continued support for well-regulated dispensaries. Just three weeks ago, Oakland city officials issued preliminary approvals for four new medical marijuana dispensaries, which would bring the total to eight.