Updated at 10:45am Pacific with Lyft’s response.

In a regulatory blow to Uber and Lyft, the California Department of Motor Vehicles has ruled that the services’ drivers’ cars have to have commercial license plates.

In a little-seen ruling issued earlier this month that was noted by the San Francisco Business Times, the California DMV ruled that “any passenger vehicle used or maintained for the transportation of persons for hire, compensation, or profit is a commercial vehicle. Even occasional use of a vehicle in this manner requires requires the vehicle to be registered commercially.”

The ruling would require any vehicles affected to convert from normal license plates to commercial plates.

In California, ride-sharing services like Uber and Lyft are regulated by the state’s Public Utilities Commission (CPUC).

In a statement to VentureBeat, Lyft made it clear it disputes the DMV’s decision. “Requiring Lyft drivers, including those who drive just a few hours a week, to get commercial plates would essentially treat peer-to-peer transportation the same as a taxi,” Lyft said, “undermining the thoughtful work done by the CPUC to craft new rules for ride-sharing in California.”

For its part, Uber spokesperson Eva Behrend told VentureBeat that the CPUC allows its drivers “to use personal vehicles with personal registration on the uberX platform. Earlier this year, Governor Brown and the California Legislature agreed with the CPUC when they passed a … bill that affirms that … drivers may use personal vehicles.”

California law defines services like Uber and Lyft as a “transportation network company,” stating that they are an “organization, including, but not limited to, a corporation, limited liability company, partnership, sole proprietor, or any other entity, operating in California that provides prearranged transportation services for compensation using an online-enabled application or platform to connect passengers with drivers using a personal vehicle.”

In addition, the CPUC states that a transportation network company “is defined as an organization, whether a corporation, partnership, sole proprietor, or other form, operating in California that provides transportation services for compensation using an online-enabled app or platform to connect passengers with drivers using their personal vehicles. The primary distinction between a TNC and other TCPs is that a TNC connects riders to drivers who drive their personal vehicle, not a vehicle such as a limousine.”

The DMV form required for converting a vehicle from normal to commercial registration has no check-box for ride-sharing services. The closest it gets is “taxi,” with the other choices being “bus,” “station wagon,” “rental limousine,” or “ambulance.”

The form also requires vehicle owners to come to the DMV in person with “a weight certificate from a Public Weighmaster.” It also states that California will begin collecting weight fees, which it does not specify, “from the date you first begin using the vehicle commercially.”