As sort of alluded to above, it's illegal to use crews from outside Portugal to operate Portuguese based planes in the event of a strike.
I'm led to believe the Portuguese government body in charge of looking after workers rights were on hand to stop crew that weren't based in Portugal operating.
Also, a number of flights were operated "on schedule" but with no passengers on board. Just the pilots. Some passengers reported that they were told that no compensation was due as the flight operated and wasn't cancelled...if that's true I'd like to see the lawyers get hold of it.