If one is called to do flights in another country where colleagues are on strike, then by law you cannot refuse.
Under which law do the 'self-employed' contractors work? A friend of mine, who is one, was once confused, and wondered what he might have to do if necessary, because his agency contract said it was subject to English law, where the agency is based, but his Ltd. company is based in Ireland. In this cross border matter where would a contractor stand?