NEW YORK (AP) — The use of cellphone location data by law enforcement agencies is “shrouded in secrecy” even though it has become widespread throughout the country, the American Civil Liberties Union said Wednesday in demanding the agencies disclose how they collect and use the data.

The civil rights organization said 34 of its affiliates around the country have filed open-records requests with hundreds of law enforcement agencies seeking disclosure on cellphone location data, which can be used to pinpoint where people go with their phones.

“We have a lot of questions about how people are tracked in this country,” said Catherine Crump, staff attorney for the ACLU Speech, Privacy and Technology Project. “Technology is an increasingly powerful way to engage in surveillance.”

She said law enforcement officials should be required to demonstrate probable cause and get warrants before tracking cellphone locations.

“We need to make a decision: Either law enforcement agents are going to be able to track us wherever we go or we are going to set up some ground rules,” she said.

ACLU affiliates want to know procedures for accessing cellphone location data, including whether law enforcement agencies have to demonstrate probable cause to obtain warrants for access. They also are requesting statistics on how often law enforcement agencies get the data and how much money is being spent on tracking cellphones.

Location information can be collected in various ways, such as by tracing a cellphone’s signal to nearby towers or by using satellite data from GPS chips embedded in an increasing number of phones. The Federal Communications Commission requires carriers to provide location information to public safety agencies when 911 calls are placed.

The first vice president of the New Jersey State Association of Chiefs of Police, Raymond Hayducka, said the use of cellphone tracking technology had become routine in many investigations.

“Every week we get some kind of crime where we have to do some kind of tracking,” said Hayducka, the chief of the South Brunswick Police Department.

He said his department would comply with the open-records request from the ACLU.

He said examples of non-criminal cases in which police have used cellphone tracking include locating people lost in the woods and finding people who made 911 calls but hung up.

In New Jersey, he said, the use of cellphone location data in higher-level criminal cases is limited and investigators first have to obtain communication data warrants from a judge.

“It’s done for a legitimate law enforcement purpose,” he said. “There’s no other reason to do it.”

Congress is considering a bill to force police to obtain warrants before collecting cellphone location information.