The U.S. Marshall Service, the Drug Enforcement Administration, and the Internal Revenue Service conducted a raid this morning on Oaksterdam University, the Oakland-based technical school that trains future "potpreneurs." The San Francisco Chronicle has more:

The university has been cordoned off by yellow caution tape.

Arlette Lee, an IRS spokeswoman, said she could not say why the agents were there other than to confirm that they were serving a federal search warrant.

"Everything's under seal," Lee said, referring to the search warrant and documents relating to the investigation. "We're not able to comment as far as the nature of this ongoing investigation."

The federal agencies are conducting a joint investigation, she said.

The raid comes fewer than three weeks after Oakland city officials issued preliminary approvals for four new medical marijuana dispensaries, even as federal prosecutors exerted increased pressure on medical cannabis dispensaries, forcing hundreds to close.

Federal officials say they are concerned about dispensaries that are getting too big or too close to parks or schools. They have long asserted that federal law trumps the state's 1996 voter-approved law legalizing medical cannabis.