I cannot see how he can sack striking crew without offering them their jobs back with compensation providing the strike is legal.
I am married to a senior union rep in a different industry and I am told that strikers cannot be sacked for striking if the strike is deemed legal (which it would be if it gets that far) if strikers are sacked they may well have to go through the courts and would get compensation and/or their jobs back.
I think the fact that they may well be able to get their jobs back is the issue here.