Southwest Airlines and Boeing face a lawsuit claiming they conspired to cover up issues with the grounded 737 Max aircraft.
Eleven customers are suing, claiming they would not have flown on the planes if they had known about suspected design flaws.
Those problems are linked to fatal crashes in Indonesia and Ethiopia.
The customers want refunds for tickets they bought on Southwest.
They also want the lawsuit declared a class action, a move that could add thousands more people and other airlines to the lawsuit.