The ACLU today filed a federal lawsuit against Allegheny County and University of Pittsburgh police, alleging that officers arrested a Pittsburgh man for using his cell phone to record an interaction between officers and one of his friends.

Elijah Matheny, of the Hill District, was arrested on April 29 and charged with violating Pennsylvania wiretapping laws. Police said he recorded an incident without officers' permission.

"The First Amendment guarantees people a right to record police officers' behavior in public places, and this right is vital to documenting and discouraging police misconduct," said Witold Walczak, the state legal director for the American Civil Liberties Union of Pennsylvania.

According to the lawsuit, Mr. Matheny and a friend were in Oakland looking for items discarded by Pitt students who were leaving for the semester. Police were called, and an officer approached Mr. Matheny and a woman he was with. Though they identified themselves, police were unable to trace the woman's background immediately, and they put her in handcuffs. As the interaction was going on, Mr. Matheny took out his cell phone and began recording.

After the woman's identity was confirmed, the lawsuit said, police took the handcuffs off. However, they arrested Mr. Matheny, telling him that they had not given permission to be recorded.

The county is named in the suit because after the initial arrest, officers called the Allegheny County District Attorney's office to find out if charges should be pursued. The on-duty prosecutor gave the go-ahead.

The case was dismissed by a judge in July.

The lawsuit cites claims for both First and Fourth Amendment violations, including that police retaliated against Mr. Matheny for legally gathering information about police activities.

The case was filed just a month before thousands of people are expected to descend on the city to protest the G-20 economic summit.

"You can be sure demonstrators and bystanders alike will be using cell phones to record police activity at the G-20, especially if there are any problems," Mr. Walczak said. "Police have every right to arrest people if they destroy property or block passage, but police need to understand that they cannot arrest people simply for putting them on candid camera."