@No RYR for Me:
In spain there is the distinction between civil servants (police for example) who have a job for life and rather low salaries and public workers who are hired by companies owned by the state. They have no guaranteed job but their salaries tend to be more in line with market standard. Spanish atco's belong to the second group.
In any case don't worry too much about Spain going on strike. To my knowledge spanish atco's have not had a strike for the last 10 years. In summer 2010 we voted to go on strike but this was later cancelled through negotiation. In september 2010 there was a general strike in Spain but atcos chose not to participate... and they got nevertheless minimum services ordered of 110%. As for the events in december 2010 the courts are still on it but it looks increasingly like it was a AENA HQ / Government instigated action.