Belgian air traffic controllers continued strike action on Wednesday, forcing the cancellation of flights at Brussels airport as it struggles to get back up to capacity after the March 22 suicide bombings.

Belgian flag carrier Brussels Airlines said that around 50 of its flights to and from the main international Zaventem airport were canceled.

The strike action over pensions and staffing has been brewing for months but the stoppage came without warning Tuesday afternoon as controllers called in sick, saying they were unfit to work.

The International Air Transport Association condemned the move, calling it "a kick in the teeth for all the airline and airport staff who have worked so hard to reconnect Brussels to the world after the appalling terrorist attack just three weeks ago."