Some 200 flights were cancelled -- about half of the total scheduled for the day -- after around a hundred flights were axed yesterday. The airport said in a tweet that it was "still unclear" whether there would be more cancellations into tomorrow.
Staff from Belgium's air traffic control organisation Belgocontrol were protesting the terms of a labour contract, including the decision to delay the effective retirement age to 58 instead of the existing 55.
Controllers "said they were sick" and unable to work, according to a statement from Belgocontrol, which said it "was looking for operational solutions".
Prime Minister Charles Michel told Belga "a handful" of workers were "taking the country hostage" just when "the image and economy of the country is under threat" following the jihadist attacks that hit the airport and Brussels' metro.
Also Read
Belgian authorities have been the subject of international criticism for their failure to prevent the coordinated suicide bombings on March 22 that killed 32 people.
It will take months to repair the departure hall and full operations are not expected to resume for weeks.
In Geneva yesterday, the International Air Transport Association condemned the strike as a "kick in the teeth for all the airline and airport staff who have worked so hard to reconnect Brussels to the world".