Poland’s simmering industrial dispute over working conditions for air traffic control staff threatens to disrupt more than 600 flights a day if a deal can’t be reached, Europe’s airspace-management body warned Friday.

Capacity for services to Warsaw could be cut to just 170 a day if the situation worsens, leaving around 340 at risk of cancellation, while 300 of 700 daily overflights via Polish skies would need to be rerouted, Eurocontrol said Friday.

The Brussels-based agency said in a statement it’s examining how to minimize the impact of walkouts but that options have been limited by “the impact of the war in Ukraine on the airspace availability.”

The drastic curbs on flights could be implemented by Poland’s Civil Aviation Authority from May 1 as disruption reaches critical levels, Eurocontrol said. Talks with unions resumed Friday in a bid to resolve a spat that erupted earlier this month over single-person operations at some control centers, with flights delayed or canceled as staff limit working in protest at the changes.

“In the event that a solution cannot be reached, this will have very negative consequences on the European aviation network,” Eurocontrol said.

Airlines facing potential dislocation including flag-carrier LOT Polish Airlines SA and discount operators Ryanair Holdings Plc and Wizz Air Holdings Plc.

The European Commission is closely monitoring the dispute, which threatens to impact flights across the bloc, spokesman Stefan de Keersmaecker told reporters Friday. The European Union executive arm has no powers to intervene but has “strongly called on all parties to urgently find a solution,” he said.