ROUGHLY HALF OF the money raised to oppose a ballot measure to legalize recreational marijuana in California is coming from police and prison guard groups, terrified that they might lose the revenue streams to which they have become so deeply addicted.

Drug war money has become a notable source of funding for law enforcement interests. Huge government grants and asset-seizure windfalls benefit police departments, while the constant supply of prisoners keeps the prison business booming.

Opposition to the marijuana legalization initiative, slated to go before voters in November, has been organized by John Lovell, a longtime Sacramento lobbyist for police chiefs and prison guard supervisors. Lovell’s Coalition for Responsible Drug Policies, a committee he created to defeat the pot initiative, raised $60,000 during the first three months of the year, according to a disclosure filed earlier this month.

The funds came from groups representing law enforcement, including the California Police Chiefs Association, the Riverside Sheriffs’ Association, the...