Spirit Airlines has announced the cancellation of even more flights through Thursday due to the strike by pilots, which started on Saturday.

To help passengers with the cancellations, the carrier says that they will be given flight credits for the full cost of their tickets, as well as an extra $100 credit to use on future flights. However, customers can also choose to get a full refund.

On Saturday morning, hundreds of pilots began industrial action after talks over pay failed with Spirit Airlines. The two sides tried to reach an agreement through the night, but were unable to come to a resolution. Airline Pilots Association head of the Spirit unit Captain Sean Creed said that the Spirit Pilot Master Executive Council called for and instituted a strike against management just after 5am.

In response to the decision, Spirit Airlines initially canceled all of Saturday’s flights. In a statement to customers on their website, the carrier says that they are working with the union to reach an equitable and fair deal that ensures the company’s long-term stability and allows them to continue offering ultra-low fares.

This whole dispute has been going on for years, with the pilots complaining that they are paid much less than those who work for other American rivals. In a statement, the Airline Pilots Association said that the strike comes after almost 4 years of negotiations and many attempts by the piloting staff to find middle ground with the airline’s management to avoid exactly this. All of the pilots, particularly first officers, have been getting only below-market rate pay for years, the statement added.