Employees at Berlin and Hamburg airports staged walkouts on Monday in an ongoing dispute over salary raises, leading to flight cancellations in both German cities.

In Berlin, all 220 departures and 70 out of 240 incoming flights were canceled, German news agency dpa reported. Due to a walkout announced at short notice by trade union ver.di, the airport in Hamburg announced in the early morning that 50 of 160 departures had been canceled.

The walkouts started at 3:30 a.m. and were supposed to last until midnight.

The union wants to increase pressure on employers with whom it is negotiating bonuses for special working hours, for example at weekends, and rules on overtime pay.

At Berlin’s BER airport, employees in the aviation security area, passenger control and personnel and goods control went on strike on Monday. Since passengers cannot be checked and then allowed into the security area without these employees, the airport had to cancel all passenger flight departures.

The union has staged frequent walkouts over recent months — three at Berlin airport this year so far — to underline its demands, with local transport, hospitals and other public services hit.

On the weekend, German government officials and labor unions reached a pay deal for more than 2.5 million public-sector workers, ending a lengthy dispute and heading off the possibility of disruptive all-out strikes. That agreement did not include airport employees, however.

For Wednesday, ver.di union announced further walkouts for local public transportation companies in the states of Schleswig-Holstein, Lower Saxony, North Rhine-Westphalia, Bavaria and Baden-Wuerttemberg, where no agreements have been reached yet.