The courts have ruled on this.
In our current climate, it's important to know what the law says and what your rights are. If an officer requests that you exit your vehicle, are you breaking the law if you refuse? In the US, no. No laws are broken if the officer says, “Would you mind stepping out of the car, ma'am?” and you say, “No, thank you.”
However, if an officer orders you out of the car and you refuse, you can be arrested for refusing to obey an officer's lawful order. The specific crime will depend upon the local statute's verbiage, but it will probably be something like “disobeying a peace officer” or “obstructing a peace officer.”
No laws are broken if the officer says, “Would you mind stepping out of the car, ma'am?”
An officer's authority to order a driver out of a vehicle at the officer's discretion comes from the US Supreme Court's ruling in Pennsylvania v. Mimms, 434 U.S. 106 (1977). That authority was extended to include ordering a passenger out of a vehicle in Maryland v. Wilson, 519 U.S. 408 (1997).
Note that the officer is not required to have probable cause or even reasonable suspicion of another crime before ordering a vehicle's occupant(s) out of the car. It is also important to note that the officer may order a vehicle's occupant(s) back into the vehicle, as well.
You can be arrested for refusing to obey an officer's lawful order.
This is, of course, assuming that an officer has already lawfully stopped you for a traffic violation or Terry stop. Yes, police officers in the US must have reasonable suspicion or probable cause to stop the driver of a motor vehicle (except when part of a traffic safety or DUI checkpoint, which have their own particular set of rules). Once that stop is made, however, the officer may order the occupant(s) out for any reason and you could be charged with a crime for disobeying.
Christopher Hawk is a retired police officer, having served for 23 years as a police officer in Illinois. His career achievements include re-writing his department's policies and training programs for Community Policing, general traffic enforcement, and DUI enforcement. He was recognized by the State of Illinois for his DUI enforcement efforts over the course of his career. He was a Field Training Officer for 20 years and spent 13 years as a Police Cyclist Instructor for the International Police Mountain Bike Association. Chris now lives in Ohio, where he drives a school bus and works on his vintage Volkswagen Type III Fastback.