BERLIN (AP) — Thousands of flights to and from German airports were canceled Friday as workers walked out to press their demands for inflation-busting pay increases.

The strikes at seven German airports, including Frankfurt, Munich and Hamburg, affected almost 300,000 passengers and forced airlines to cancel more than 2,300 flights.

Christine Behle of the Verdi labor union told public broadcaster RBB-Inforadio that failure to reach a meaningful deal with employers on pay could result in a “summer of chaos” at German airports.

The union is seeking a 10.5% increase for its members, or at least 500 euros, to make up for high inflation seen in Germany and elsewhere last year due to the knock-on effects Russia’s attack on Ukraine has had on global food and energy prices.

Verdi chairman Frank Werneke told weekly Frankfurter Allgemeine Sonntagszeitung that the willingness among its members to stage strikes was big and future walkouts could reach “another dimension.”

He noted that recent strikes at airports, public transport and childcare facilities could be extended to garbage removal services and hospitals.