The Serbian flight controllers union warned on Tuesday of violations of their rights, adding that they could launch a strike.

The union said in a statement that the Serbia and Montenegro Air Traffic Services (SMATSA) is violating employee rights and endangering the safety of flights in the airspace over Serbia and Montenegro. It added that international institutions and the European transport workers union had been informed of the problems.

The union said that standard operating procedures have not been followed for a long time increasing the stress experienced by air traffic controllers and added that working hours have been changed in violation of the law.

“The working hours are the same in full season and at other times and controllers are often overworked with no adequate space for rest,” it said.