Ryanair Holdings Plc grounded dozens of flights Thursday as pilots in its Irish home market walked out after failing to agree new contracts as part of a move toward unionization at the discount giant.

As of 6 a.m. local time, Dublin Airport’s website listed as canceled departures to 16 cities including London, Birmingham and Manchester, England, with a similar number of arrivals also scrapped. Ryanair had said it would cancel up to 30 of its 290 flights at Irish airports during the 24-hour labor action. The airline didn’t reply to requests for further comment.

Ireland’s Forsa union said on Twitter that its members at the Irish Air Line Pilots’ Association began the walkout at 1 a.m. as planned.

While the strike is the biggest Ryanair has had to face, the carrier said in a statement that the impact will be “limited,” with all customers due to travel on affected services offered alternative flights, ferry bookings or a refund. The trips scrapped are all on short routes to the U.K. where the airline generally has multiple daily frequencies, helping to minimize the strain on the network.

Forsa had said late Wednesday that talks with Ryanair had ended after seven hours of talks with “very little progress.” Negotiations got no further than a discussion of seniority issues and the possibility of establishing a working group, spokesman Niall Shanahan said.

Second Strike

The strike is only the second by employees of the airline after pilots in Germany walked out for a few hours in December without major disruptions. Ryanair has become more vulnerable to industrial action after a staffing crunch last year forced it to recognize trade unions, though Chief Executive Officer Michael O’Leary has said he’s prepared to endure disruption rather than bend to union demands that would threaten the low-cost business model.

As many as 120 Ryanair pilots were balloted on industrial action, according to the Irish Air Line Pilots’ Association, though it’s not clear how many are rostered for duty during the strike and what proportion of those will walk out. Ryanair said only 27 percent of pilots will walk out, and blamed Forsa for rejecting its overtures in talks.

Germany’s Vereinigung Cockpit pilot union is also balloting Ryanair members in a dispute over pay and working conditions, with the outcome due later this month. Spanish, Portuguese and Belgian cabin crew are due to strike on July 25 and 26, with Italian flight attendants joining the action on July 25. And IALPA has said it plans to notify Ryanair of additional walkouts “in due course.”