The Harborside Health Center, the biggest dispensary in Oakland, claims more than 100,000 customers, 100 employees and $20 million in annual marijuana sales, the Oakland Tribune reported.
U.S. Attorney Melinda Haag has filed civil forfeiture complaints against Harborside's landlords as federal prosecutors target California's medical marijuana industry.
The Tribune said federal prosecutors have forced hundreds of California dispensaries to close by citing state violations for being within 1,000 feet of schools, parks and playgrounds.
Haag said in a statement Wednesday she was now focusing on "marijuana superstores" like Harborside that aren't close to areas where children gather.
"The larger the operation, the greater the likelihood that there will be abuse of the state's medical marijuana laws," the statement said.
Dale Gieringer, director of California NORML, criticized the attempt to seize Harborside properties.
"This is just a naked coming out that they're going after the most successful players no matter how responsibly they have acted," Gieringer said.
Anna Chretien, who owns Harborside in Oakland, did not return calls Wednesday, the Tribune said.
A federal complaint estimated the Oakland property, where Chretien also runs a security firm, is worth $1.8 million.
In a message on its Web site Wednesday, Harborside said it's not in danger of imminent closing.
"We will contest the Department of Justice action openly and in public and through all legal means at our disposal," Harborside's Executive Director Steve DeAngelo said in a statement. "We look forward to our day in court and are confident that justice is on our side."
Harborside also has a dispensary in San Jose.