The firefighters’ union has filed suit against Mayor Toni Harp in state Superior Court over an appointment that the union claims contravenes the city charter and collective bargaining law.

Last week  Harp appointed firefighter Michael Briscoe to head the city’s 911 emergency communications center. Local 825, the union representing Briscoe and his more than 300 colleagues in the New Haven Fire Department, is arguing that the appointment violated the city charter, which allows the mayor to assign an employee of one department to the temporary performance of “similar duties” in another department.

“The duties of a line firefighter and the Director of Public Safety are not similar,” said Local 825 President James Kottage. “We’re not going after Michael Briscoe. We’re going after the process.”

The legal complaint, prepared by attorney Patricia Cofrancesco and submitted Thursday afternoon, further alleges that Harp violated collective bargaining law by dealing directly with Briscoe, rather than going through union leadership. Kottage said he is the only person with the discretion to change the terms or hours of his members’ employment.

The emergency communications position should be civil-service tested, Kottage added, and it should have been posted to allow all interested parties to interview for the job. If Briscoe had resigned as a firefighter and left the union, he added, the appointment would have been lawful.

“The mayor is trying to say [Briscoe] is still part of the union, but executive management is clearly non-union,” Kottage said.

Kottage’s union endorsed Harp in last year’s mayoral election, and he said Friday he stands by that decision. “I’ll give her the benefit of the doubt, but not for long,” he said.

In a Friday statement, City Hall Spokesman Laurence Grotheer suggested that the duties of the two positions are sufficiently similar to justify the appointment, saying that the transfer affirms the skills of the city’s public safety personnel.

Grotheer said the city is willing to discuss further labor protections with the union. He did not specifically refute the the union’s legal claims.

In a March 31 letter addressed to Briscoe, Harp offered him the director’s position on a temporary basis until his term with the Fire Department ends in October 2015. At that point, she said, the city would hire him full-time as Director of the Department of Public Safety Communications with a salary of $98,000 and other benefits. In the interim time, the letter states, Briscoe will remain a member of Local 825 and be entitled to all the benefits of a Local 825 member, including healthcare and pension.

“I’m trying to wrap my head around why a union would want a member replaced by an outsider,” Briscoe’s attorney, David Rosen LAW ’69, said in a Friday email. He said he could not comment further before looking at the suit.

The city’s police union has also filed a complaint over Briscoe’s appointment, but with a state labor board. The police union is arguing that a police officer should head the center, which manages hundreds of thousands of emergency calls each year.

Briscoe was until recently locked in a legal battle of his own with the city, having filed a discrimination suit arising from lieutenant promotions based on a 2003 exam. Briscoe agreed to settle the suit for $285,000.