Philadelphia’s rowdy union politics may cause travel hassles for convention-goers. After a rolling vote on Tuesday, contracted airport workers decided to hold a walk-out during the Democratic National Convention.

The walk-out could include as many as 1,000 workers, including baggage handlers, cabin cleaners, customer-service assistants and gate agents. They have demanded to unionize and receive a $15 minimum wage, and also are calling for changes to scheduling, sick pay and disciplinary policy. The precise details of the walk-out, including the dates, have not yet been announced.

Service Employees International Union 32BJ, which is organizing the potential walk-out, has endorsed Hillary Clinton. Julie Blust, a Philadelphia-based spokeswoman for the union, tells Heat Street that “the intention is not to hurt the DNC.”

“The timing is such that you have the national and international spotlight on Philadelphia,” Blust says. “The workers feel like this is their opportunity. And the people coming to the DNC are our natural allies.”

But Kevin Gillen, a senior research fellow at Drexel University’s Lindy Institute for Urban Innovation in Philadelphia, says the traditional alliance between the Democratic party and Pennsylvania’s powerful organized labor is wearing thinner than usual this year.

In particular, white, blue-collar workers in Pennsylvania’s building-trades sector have been put off by some of the Democrats’ environmental stances, which they view as anti-growth and a threat to their jobs.

“A lot of them are seeing the convention as an opportunity to raise these grievances,” says Gillen.

On Wednesday afternoon, Philadelphia’s mayor, James Kenney, issued a statement in support of the airline workers’ walk-out.

“While we don’t anticipate these demonstrators will interfere with Airport service during the DNC, that fact does not make these working conditions any less of an issue,” Kenney said. “Supporting these workers in not just the right thing to do for the DNC, it’s the right thing to do.”

Kenney’s position is perhaps unsurprising, given that, between 2013 and early 2015, his mayoral campaign received more than $500,000 from organized labor.

But it may signal that more unions are eying ways to use the threat of DNC disruption to secure local victories.

In Philadelphia, that could get scrappy.

The city’s labor unions—dominated by the building trades—have a long history of using violence, vandalism, intimidation and harassment to get their way. Highlights of their recent hijinks include union members attacking non-union construction workers with baseball bats; torching a Quaker meeting house and causing $500,000 in damage over a labor dispute; and deploying drones at a worksite that couldn’t afford to use solely union workers.

And last time Philadelphia was in the international spotlight, during the Pope’s visit, labor tensions also flared.

Philadelphia’s powerful electrical workers’ union, Local 98, went on strike, disrupting news coverage. Rumors abound of rougher activities, too—but, as usual in a labor climate known for intimidation, they remain unconfirmed.

— Jillian Kay Melchior writes for Heat Street and is a fellow for the Steamboat Institute and the Independent Women’s Forum.