Spirit Airlines and its striking pilots agreed to meet with mediators on Tuesday, the union said, signaling a potential thaw that would be welcomed by the thousands of customers holding tickets on the grounded airline.

Sean Creed, the head of the pilots' union at Spirit, said the National Mediation Board had asked both sides to meet in Fort Lauderdale, Fla. However, union officials say the strike will continue until they approve a deal.

Spirit said it wouldn't fly until Thursday at the earliest, forcing its roughly 16,000 daily passengers to get where they were going by rental car or an expensive walk-up fare on another airline. Spirit carries just 1 percent of the nation's air traffic, but those travelers have been 100 percent grounded by the walkout.

Spirit is usually the biggest carrier at Atlantic City International Airport in New Jersey.

The airline is offering customers credit for future flights, plus $100. But if they want refunds instead, customers have to call the airline and ask for one.

Spirit aircraft have not flown since pilots walked out on Saturday in a pay dispute. Just a few days before the strike, it was saying publicly that it would fly through it. That didn't happen. It has said it would try to get passengers onto flights on other airlines. Spirit spokeswoman Misty Pinson declined to say on Monday how many passengers had gotten seats on other carriers with Spirit's help.

Joe Brancatelli, an air travel expert who runs a travel blog, said Spirit's policy of encouraging credit for future travel rather than a refund made it harder for customers to get their money back.

"Everything they've done maximizes the pain on the passenger, minimizes their financial exposure," he said.

Spirit has said that its last offer would have raised pilot pay by 29 percent over five years, although pilots would have to work more to get that money. Pilots have been negotiating for more than three years, and they've said that the proposed raise works out to less than 4 percent per year.