St. Paul Police Chief Todd Axtell was reviewing several videos captured by his officers' body-worn cameras earlier this year when he noticed the sound was cut off when officers spoke to their supervisors at active scenes.

"I remember scratching my head wondering why a muting had occurred," Axtell said Wednesday. "We have nothing to hide, so we shouldn't act like we have something to hide."

Axtell changed the old policy, which had allowed muting in some circumstances, and banned it. The department also disabled the mute function on all of its body-worn cameras.

His officers hit back. The St. Paul Police Federation — the union representing rank-and-file officers — has filed a lawsuit asking a judge to put an immediate stop to the new policy and find Axtell in violation of labor practices.

The lawsuit, which names Axtell and the city of St. Paul as defendants, claims that the changes Axtell announced in June could jeopardize officers' safety.

"There are things about their jobs that they're privy to that we shouldn't be," said federation attorney Chris Wachtler. "It's just stuff that shouldn't be accessible by those who would attempt to interfere with law enforcement or thwart the efforts of law enforcement to prevent crime."

Under the original policy, muting was allowed when there was a need to discuss "specialty tactics for resolving a dynamic scene," or investigative techniques where the tactic "is not readily known to the public and where disclosure of the tactic or technique could jeopardize its future," according to the lawsuit.

Police spokesman Steve Linders said that officers were required to verbally note that they were going to mute their cameras before using the function, and were supposed to document it later in writing.

In the first six months of 2018, the department received 89 requests for body-worn footage from people who were the subject of the recording, Linders said. Not all requests were granted, although that exact number wasn't immediately available Wednesday.

The department released 136 videos through the public requests, which sometimes included multiple videos from the same incident, Linders said.

The federation wrote Axtell a letter dated July 7 expressing opposition to the changes, which went into effect June 26, and asserting that he violated labor practices within the Minnesota Public Employment Labor Relations Act.

According to the lawsuit, Axtell responded on July 19 stating that the city disagreed with the federation, and that the changes were not subject to collective bargaining.

Axtell said Wednesday that no one incident prompted the changes.

"Since becoming chief, I made a commitment that transparency would be our top priority," he said. "As I take a look at incidents across the country … it occurred to me that having a mute policy was not consistent with our commitment to transparency."

Axtell said that the muted videos he observed earlier this year were allowed within the old policy's criteria. The new policy remains in effect.