On June 12, 2010, Spirit grounded its flights when its unionized pilots walked out on strike, stranding thousands of passengers.[14] The ultimately successful pilot strike came after more than four years of inconclusive negotiations between the airline and the Air Line Pilots Association (ALPA), which represents Spirit's pilots. On June 15, negotiations between the airline and ALPA resumed, and a tentative agreement was reached late in the evening on June 16. The tentative agreement, which Spirit pilots later ratified by a 74% margin, brought the Spirit pilots' compensation and benefits in line with comparable U.S. Airbus operators. Flights eventually resumed.[15] Of particular note, is that this was the first legal industrial action (strike) by U.S. ALPA represented pilots since 2005 (Polar Air Cargo), and the first passenger airline strike by U.S. ALPA represented pilots since 2001 (Comair).
https://en.wikipedia.org/wiki/Spirit_Airlines