(CNN) -- Swedish pilots went on a one-day strike Wednesday, the chairman of the Swedish Airline Pilots Association, Gunnar Mandahl, told CNN.
The dispute is mainly about regulating the hiring of external staff, he said.
"At one of the four regional airlines concerned, they fired all of their pilots and said they wanted to externally hire everyone instead," he said. "But in Sweden, if you are going to fire staff it has to be because of a lack of work, and it is bogus to claim that in this case. They just wanted to bypass the existing laws and regulations."
The dispute is also over pilots' salaries, according to Swedish news agency TT.
A total of 1,300 active pilots have gone on strike, most of them in sympathy with the pilots at the affected airlines.
The sympathy strike was set to continue until 7 a.m. ET, while the pilots at the heart of the dispute planned to be on strike until 5 p.m. ET.
A total of 23.000 passengers will be affected on a total of 230 cancelled domestic and international flights, according to TT.
"This strike will severely affect the airlines, and their customers and it will unfortunately contribute to a deterioration in people's confidence in the Swedish airline industry," Peter Jeppsson, director-general of The Transport Group, said in a statement on the employers' association's website.