Not only does a feature of a popular Google Inc. mobile app put police officers' lives in danger, it also interferes with law enforcement's ability to carry out its speeding ticket mission, a leading group of sheriffs said this week.

The National Sheriffs' Association had previously focused its campaign against Waze on police safety after the fatal shootings of two New York police officers in December.

Waze is a user-sourced traffic and navigation app, but it also allows users to tag the locations of parked police vehicles, accidents, congestion, traffic cameras, potholes and more, so that other drivers using the app are warned as they approach the same location.

The ability to mark police vehicle locations, however, is a problem for the sheriffs' association.

The group broadened a campaign against Waze with a new statement criticizing Google's software as hampering the use of speed traps. The trade association said radar guns and other speed enforcement techniques have reduced highways deaths.

"This app will hamper those activities by locating law enforcement officers and puts the public at risk," the group said.

In a twist, the newly expressed concern about speeding is also Google's own defence of its software.

Popularity spiked after law enforcement concerns

"Most users tend to drive more carefully when they believe law enforcement is nearby," Waze spokeswoman Julie Mossler said.

Waze actually gained popularity in the last week since The Associated Press first disclosed law enforcement's concerns, climbing four positions to No. 8 on Apple's ranking of the top free mobile apps.

'Waze represents person-to person information in the public square. And that's long been a U.S. right under the Constitution.' - Nuala O'Connor, head of the Center for Democracy and Technology

The Los Angeles Police chief and the executive director of the Fraternal Order of Police have echoed the sheriffs' concerns about police safety but have not said anything about the app interfering with catching speeders.

Sen. Charles Schumer, a Democrat, who in 2011 raised issues with mobile apps that identified drunken driving checkpoints, is concerned about the Waze app police-reporting feature, according to his office.

Other major police trade groups had not yet formally joined the sheriffs' campaign. Some police departments near San Francisco, where Google is headquartered, did not share the same concerns.

Heather Randol, a spokeswoman for the San Jose Police Department, said the department does not have much information about the software's impact.

"However, part of our police model includes a highly visible police presence to reduce crime," Randol said.

Police icons show up on maps

Waze users mark locations of police vehicles — which are generally stopped in public spaces — on maps without much distinction other than "visible" or "hidden." Users driving nearby see a police icon, but it's not immediately clear whether police are there for a speed trap, a sobriety check or a lunch break.

Police objections to Waze add new complexity to the debate about technology and privacy. Some Waze supporters lashed out at outspoken sheriffs on social media, pointing to the irony of police concerns about being watched amid sensational disclosures about police and government surveillance of citizens.

Sheriff Mike Brown of Bedford County, Virginia, said states might pass laws to prevent people from revealing the locations of parked police cruisers. Privacy advocates, however, said First Amendment protections will stand in the way.

"Waze represents person-to person information in the public square," said Nuala O'Connor, head of the Center for Democracy and Technology, a Washington civil liberties group, who said she uses the software. "And that's long been a U.S. right under the Constitution."

There are no known connections between any violent attack on police and the Waze software. But Brown and others believe it is only a matter of time.