All this has to do with employment of people with disabilities and the systems that ensure a number of posts are reserved to them.

I think this is referring to staff who are exempt from participating in union action - e.g., management or positions deemed essential, either by contract or by some tribunal. Excluded staff is a term often heard in strike situations. These are people in staff positions who are permitted (or required) to cross picket lines in order to maintain a minimum level of service or to perform essential services. We have a fair number of labour strikes in this neck of the woods.