Like Uber ride share or Airbnb accommodation rentals before it, a new mobile app driven by user sharing is running into increased legal scrutiny.

Waze, which tracks the movement of cars in traffic in real time to direct users to quicker routes, is being challenged by law enforcement groups. They say one feature – which warns users when police are nearby – puts officer lives in danger.

At a meeting of the National Sheriffs Association in Washington Friday, Sheriff Mike Brown of Virginia's Bedford County called the feature a “police stalker” and told the gathering it presents a danger to law enforcement, according to the Associated Press.

"The police community needs to coordinate an effort to have the owner, Google, act like the responsible corporate citizen they have always been and remove this feature from the application even before any litigation or statutory action," said Mr. Brown, who serves as the chairman of the National Sheriffs Association's technology committee.

At a time of heightened public concern over ambush-style attacks on police – typified by the killing of two Brooklyn police officers in December – the free app is seen as potentially making law enforcement officers sitting ducks for criminals. The controversial feature shows the location of police with a small icon of a face in a police hat.

Purchased by Google in 2013 for $966 million, Waze relies on a combination of social networking and GPS navigation. The Waze website explains: “After typing in their destination address, users just drive with the app open on their phone to passively contribute traffic and other road data, but they can also take a more active role by sharing road reports on accidents, police traps, or any other hazards along the way, helping to give other users in the area a 'heads-up' about what's to come.”

Analysts say the app raises compelling moral and legal questions.

“As an ethicist I would ask whether it’s appropriate for a smartphone app (or any other technology) to provide information that may be designed to help people break the law,” says Frederick Reamer, a professor in the School of Social Work at Rhode Island College in Providence. “How would the public feel if smartphone apps or other technology provided users with information about where police are conducting surveillance of heroin transactions or sex trafficking of minors so they can avoid detection and commit crimes?”

But police partners support Waze and its features, including reports of police presence, "because most users tend to drive more carefully when they believe law enforcement is nearby," said Julie Mossler, spokeswoman for Waze, in a statement.

"We think very deeply about safety and security and work in partnership with the NYPD and other Police and Departments of Transportation all over the world, sharing information on road incidents and closures to help municipalities better understand what's happening in their cities in real time," she added. "These relationships keep citizens safe, promote faster emergency response and help alleviate traffic congestion."

In some cases, knowing where a police officer is makes the officer safer, says Philip Stinson, an assistant professor of criminal justice at Bowling Green State University in Ohio.

“In rural highway settings, it is far safer for oncoming drivers to know where police cars have pulled someone over so they can switch to the lane away from where the cars are,” says Professor Stinson.

Indeed, the issue is not black and white, says Tod Burke, an associate dean and professor of criminal justice at Radford University in Virginia.

“This is just a modern update of what has already been out there for years – with police scanners, CB radios, and radar detectors,” Professor Burke says, noting that other social media – from Instagram to Twitter to Facebook – play the same roles.

“Courts have held that it is freedom of speech for cars to flash their lights to oncoming cars to let them know police are ahead,” he says. “The other side of this is that if I was in distress and had this device, I would know where I could go for help. That would be a huge advantage.”