The Boston Police Patrolmen's Union is asking the court to prevent the city from forcing 100 police officers to wear body cameras beginning in September.

The union, which filed the lawsuit Friday in Suffolk Superior Court, argues the city is violating their "collectively-bargained grievance arbitration process" by selecting officers to wear body cameras for a pilot program that was originally designed to be voluntary.

The union's attorney John Becker, of Sandulli Grace, says the union is not being obstructionist.

When no officer signed up for the voluntary program, he says, the city and union should have gone back to the negotiating table to try to come up with a new plan.

"The fact that we've had a glitch in terms of getting the volunteers on board, doesn't mean that they should just throw that agreement out the window," Becker says.

He argues a mandatory program is less likely to succeed than a voluntary one.

"We're in the practice of trying to move into the future in a way where everyone's rights are respected, where there are safeguards for everyone ... including the citizens of Boston as well as the members of the Boston Police Patrolmen's Union, and where the program is set up in such a way where it will be more likely to succeed," Becker says.

Becker says the request for an injunction is an attempt to put the program on hold while the issue is resolved through the grievance process.

The city has not responded to WBUR's request for comment.

The American Civil Liberties Union of Massachusetts argues that this lawsuit shows an "alarming pattern" where the union has "seen fit to demand instruments of violence and to block instruments of accountability."

"Their complaint nowhere mentions the risk that civilians, especially those in communities of color, will be harmed if this program is blocked," Chris Ott, ACLU communications director, said in a statement.

The city had been planning on a Sept. 2 roll out date for the pilot program.

With reporting by WBUR's Dave Faneuf