Refueling workers at London Heathrow airport said they would stage a 72-hour walkout over wages beginning July 21, threatening to further disrupt operations at the hub.

The Unite union said in a statement Tuesday that the Aviation Fuel Services Ltd. employees voted to strike after the company hadn’t raised wages in three years. The action affects about 50 workers, a union representative said.

AFS is a joint venture among fuel companies BP Plc, TotalEnergies SE, Q8 Aviation and Valero Energy, and supplies fuel to over 70 airlines including American Airlines Group Inc., Delta Air Lines Inc., United Airlines Holdings Inc. and Emirates, the union said. 

The latest announcement adds to the disruptions challenging the travel industry just as the peak summer season gets underway, with airports and airlines across Europe slashing capacity and canceling flights on staffing shortages and worker strikes. 

A spokesman for Heathrow said he couldn’t immediately comment on the likely impact of the refueling workers’ plans. AFS couldn’t immediately be reached for comment.

Read More: Summer Travel Chaos Hits Europe Hardest as Delays Escalate

Heathrow has been hit hard by airline labor shortages and other problems, prompting British Airways to scrap thousands of flights this summer. Check-in workers at the carrier, part of IAG SA, have also threatened to strike. 

Carriers across Europe, including SAS AB, Ryanair Holdings Plc and EasyJet Plc, have also suffered strikes.