The city of Austin and the Austin Firefighters Association are violating the Texas Constitution by paying firefighters while they’re conducting union activities, according to a lawsuit filed Wednesday by conservative groups in Travis County.

The suit, filed by the Austin-based Texas Public Policy Foundation and the Phoenix-based Goldwater Institute on behalf of Austin residents Mark Pulliam and Jay Wiley, says that a provision in the union’s contract with the city allows firefighters to spend 5,600 hours on union business “at the expense of taxpayers.” Of that, 2,080 of the hours are allocated for the union president’s use.

The Texas Constitution prohibits payment by a political subdivision to a private entity that doesn’t have a public purpose or benefit.

“In the city’s proposed budget, you have a tax increase of $150. At the same time, you have the police chief and the fire chief saying that they don’t have enough officers,” said Robert Henneke, the foundation’s general counsel. “Before we raise taxes and before we expand staff, it’s reasonable for my clients to demand that their tax dollars and the resources that the city has be focused on services for the people of Austin.”

Bob Nicks, the firefighters association president, and the city of Austin maintain that the agreement is legal. Nicks said the association is the latest target in a broad campaign against unions that have long had agreements with cities to use work time for union business.

In 2015, an Arizona appeals court sided with the Goldwater Institute after it had filed a similar lawsuit against the city of Phoenix and its police union over paying officers while doing union work.

Union activities include pay negotiations and attending dispute resolution proceedings, but Nicks said he also helps build fire stations and create public-private partnerships to reduce costs to taxpayers.

“A good deal of what we do is to add value to the community,” Nicks said. “This is quite simply a union-busting move.”

The city also allows emergency medical service officials and Austin police officers to use work time for union activities.

The lawsuit alleges that the city isn’t required to audit union leave time nor does the association require an accounting for how the time is used.

Nicks said that the Fire Department must approve and document how firefighters use union leave time.