The Las Vegas-headquartered airline has now canceled about 14 flights arriving or departing at the airport since the emergency landing of one of its aircraft on June 17 due to a pressurization problem. That was the second Allegiant emergency landing at the airport this month.

One cancellation, Flight 893, pushed away from a St. Pete-Clearwater gate Friday at 8:17 p.m. but was forced to return before takeoff due to a "maintenance" issue that the airline refused to detail.

An Allegiant flight scheduled to leave Las Vegas Monday to return to Billings was canceled, leaving 136 passengers stranded

The flight scheduled to depart from Billings to Las Vegas Monday was also canceled for 106 passengers.

Wheeler said those flights will be refunded.

Wheeler said the flights were canceled because of a mechanical problem that made it unsafe to fly.

“Airline pilots are calling on the board to put an end to the company's nickel and dime approach to managing its operation,” the letter reads.

The union cited 38 instances of “mechanical issues, including failing engines, pressurization problems, smoke in the cockpit, inoperable radar systems and failing windshield anti-ice devices,” between January and March 2015 as reasons for concern among pilots.

Wheeler said the flight cancellation is not due to a pilots strike and that the concerns addressed in the letter are nothing more than a tactic for wage negotiations.