DENVER (KDVR) — The union for Southwest Airlines flight attendants is blaming the company’s failure to upgrade software as a major reason for the holiday nightmare of canceled flights around the country.

Transport Workers Union of America Local 556 said it has been complaining for years to try and get the company to upgrade its technology as it has expanded but it hasn’t, which has resulted in crews being stranded causing delays and cancellations.

“The way Southwest Airlines has treated its flight crews can only be termed ‘despicable,’” TWU Local 556 President Lyn Montgomery said. “We know the demands of holiday travel. We know winter storms. And believe me, we know about stepping up and putting in long work hours when we are called to do so; we are flight attendants. But at this point, the many years of failure by management, despite many unions’ demands to modernize, has left flight attendants fatigued, stranded, hungry and cold – on Christmas! This impacts lives and threatens safety for all.”

The union said Southwest COO Andrew Watterson admitted its current systems are “overmatched” by the latest winter storm, but said technological improvements could have prevented employees and crewmembers from being grounded and saved customers from being stuck over the Christmas holiday travel rush.

The union also said in a statement that Southwest Airlines CEO Bob Jordan said on Christmas day, “Part of what we’re suffering is a lack of tools. We’ve talked an awful lot about modernizing the operation, and the need to do that. And Crew Scheduling is one of the places that we need to invest in.”

Local 556 has been in negotiations for a new collective bargaining agreement with the company for four years and said this is just another addition to the list of things it wants to see changed for its workers.