DALLAS (AP) — The union representing Southwest Airlines pilots is suing Boeing and calling the grounded 737 Max unsafe.

The Southwest Airlines Pilots Association said in the lawsuit filed Tuesday that Boeing rushed the plane into service and misled pilots by saying it was little different than previous versions of the 737. The union says those claims turned out to be false.

The lawsuit filed in a Texas state court in Dallas is a blow to Boeing’s plan to restore public confidence in the plane, which remains grounded after two crashes that killed 346 people.

Boeing hopes to use pilots in a campaign to reassure travelers to fly on the plane once regulators approve changes that the company is making to a key flight-control system. Southwest in the biggest operator of Boeing 737s.