The law prohibits motorists from holding their cell phones while they talk, but still allows the use of a hands-free device such as a Bluetooth or headset that does not cover both ears.
According to California Highway Patrol Sgt. Trent Cross, CHP officers, including himself, began issuing citations this morning.
Cross said he has already issued four citations himself, however, "For the most part, a large majority of the people are complying with the new law," he said.
Enforcement numbers are expected in the coming days, he said.
A second law, which also went into effect today, prohibits any driver under age 18 from talking on a cell phone at all while driving.
The base fine for violators is $20 for a first offense and $50 for subsequent offenses, but when including penalties and assessments, citations will average $76 for first-time offenders and $190 for subsequent offenders, according to the CHP.
Violations will show up on the driver's record, however the Department of Motor Vehicles will not assign a violation point.
Drivers may still use cell phones to make calls to emergency services agencies.