These are often joint operations by multiple agencies under the auspices of the CA Public Utilities Commission targeting limousine services, frequently around LAX, Hollywood, San Francisco and other "public" limo-rich areas.
"Enforcement Section staff initiate enforcement action through the Commission and through the California courts. They also coordinate closely with other law enforcement and regulatory agencies in ensuring that only safe, legal and properly inspected carriers transport passengers in California." Passenger Carriers Enforcement Unit
You'll often hear units operating outside of their normal jurisdictions (like Beverly Hills PD units in Hollywood), sometimes on unusual or patched frequencies. I believe the State of Calif picks up the entire tab.