The National Motorists Association (NMA) last week warned the US Supreme Court about the potential for court precedent to undermine the rights of passengers using ride-sharing services. The motorist rights group filed a friend of the court brief on an appeal scheduled to be heard on January 9. The Third Circuit US Court of Appeals had previously ruled that someone driving a rental car with permission can be subjected to a warrantless search simply because his name is not on the rental agreement.

"Because the Third Circuit's rule guarantees that a significant number of drivers of rental cars will be without Fourth Amendment protection, that rule creates 'sitting ducks' for potentially abusive law enforcement activity," NMA attorney Aaron M. Panner wrote. "As this case illustrates, law enforcement often can spot rental cars, which, under the Third Circuit's rule, may be subject to search even without reasonable suspicion of any crime."

In Byrd v. United States, Terrence Byrd was driving a Budget rental car near Harrisburg, Pennsylvania, when a state trooper noticed the car was a rental and that the driver had reclined his seat to an "unusual degree." The trooper ordered Byrd to pull over, and the officer after checking Byrd'spaperwork decided he did not need permission to search the vehicle. When he did, he found heroin.

The sole issue before the high court is whether the Third Circuit was right to determine that a rental car driver has no expectation of privacy if he is not listed on the rental agreement. The NMA suggests the ruling has massive implications for users of ride-sharing services like Uber and Lyft or car-sharing services like Zipcar and Car2go that do not operate on the old-fashioned model of taxi services and rental cars.

The membership-based car-sharing services allow users to take any available car on short notice. There is no paper agreement to hand to a police officer. In the ride-sharing situations, companies like Uber and Lyft do not own the vehicles, the drivers do, but the customers have their agreement with the company, not the driver.

"The variations in car-sharing companies' terms of service are unlikely to have any direct impact on whether a motorist has an expectation of privacy when she is operating a vehicle," Panner wrote. "Furthermore, their very variety -- and complexity -- demonstrate why tying Fourth Amendment rights to contractual arrangements is unworkable in many situations."

The motorist rights group is concerned that an easy ability to search rental vehicles creates an incentive for police to conduct more searches and use civil asset forfeiture to seize the cars for profit.