Federal agents on Monday raided a San Francisco-area medical marijuana training school at the heart of California's pot legalisation movement.
The doors to Oaksterdam University in Oakland were cordoned off by yellow tape and blocked by US marshals.
Agents from the Drug Enforcement Administration (DEA) carted trash bags of unknown materials out of the school to a waiting van. Arlette Lee, an IRS spokeswoman, told reporters that agents were serving a federal search warrant but said she could not otherwise comment on the purpose of the raid.
She said all documents related to the raid were under seal. About a dozen protesters gathered, demanding an end to federal crackdowns on medical marijuana.
Ryan Hooper, 26, wearing an Oaksterdam hat and sweatshirt, said he had finished taking courses at the school in February.
"This is not in the best interest of the city," Hooper said.
"If they close the dispensaries, all of this stuff is going to go back underground." Oaksterdam University was founded by Richard Lee, the main backer of the California ballot measure defeated in 2010 that would have legalised marijuana in the state for recreational use.
The neighbourhood has also been home to several medical marijuana dispensaries, including one founded by Lee. Lee did not immediately return a message seeking comment.
The city of Oakland has long allowed four medical marijuana dispensaries to legally operate under city ordinances and recently awarded permits that would allow four more to open.
At the same time, federal prosecutors across California have been working for months to shut down dispensaries by threatening to seize landlords' property if they did not evict marijuana retailers.