If you’re heading to Europe tomorrow, or if you’re there already reading this and you’ve got a Wednesday flight with Lufthansa, you’ll want to check in with the airline right about now: the German carrier announced it’s grounding 1,000 flights tomorrow — affecting 140,000 travelers — amid a pilot strike.

The pilots union, Vereinigung Cockpit, kicked off the strike starting with long-haul flights on Tuesday, which forced Lufthansa to cancel 90 flights, the airline said today. The strike is extending to include medium- and short-haul flights on Wednesday.

Subsidiaries Germanwings, SWISS, Austrian Airlines and Brussels Airlines aren’t affected, Lufthansa said.

“Lufthansa deeply regrets the resulting inconvenience to its customers and will do its best to keep possible disruptions to a minimum,” the airline said, urging customers to check its website for updates on the travel situation. Customers who have flights canceled due to the strike can rebook or cancel their reservation without penalties.

The 5,400 Lufthansa pilots are striking for a variety of issues; among those, they want the airline to continue to pay a transition payment for early retirees, notes the Associated Press, they’re against a restructuring of the airline.

The union said on Monday that an offer it made to Lufthansa that included “vast concessions on a variety of issues” that could save more than 500 million euros had been rejected, and the airline’s counter-proposal was promising at first, but later deemed “insubstantial.”

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