This can’t be considered unprofessional at all, and to call it Union Flu is totally disingenuous.
The fact of the matter is that there are times when multiple people can call sick on any day, and your employee numbers should be able to cover that. That the entire air traffic control system in this country relies so heavily on the controllers working their days off should be cause for concern. When controllers start leaving for better pastures in the Middle East, South East Asia and North America, exasperating the controller shortages, then this is probably a good indication as to the terms and conditions the front line staff work under.
Given that Airservices primary role is to provide ATC and RFF facilities - it strikes me as odd that only half the work force is made up of air traffic controllers and fire fighters. Airservices (as a wholly owned Government Enterprise) made a $75m profit last year based on revenues of close to $1.1b from airways revenue. Given the significant amount in navigation charges they pay, I don’t think it would be unreasonable for the airlines to expect that Airservices manages their labour force appropriately by ensuring adequate staffing levels (through ongoing and increased recruitment and improving Ts and Cs to retain experienced staff).
So rather than targeting individuals, it may be a little more helpful to take a bit more of a systematic look into what caused yesterday’s mess.