Are Ryanair pilots still working under 'Self Employed' contracts?
If so then I don't see how any collective union action can be done without them becoming employees and IR35 caught. Ditto if they are told to change their holidays and then do as they are told.
They may need to be careful that any action taken now does not have a knock on effect later by the taxman.
If they are to be seen as self employed then they should forget any union action and the only way forward I can see, which won't jeopardise their tax situation, is to just refuse to come in to work.