RMT strike action - WHY?

Can someone please tell me on what basis the RMTs strike action is justified. Is it just an effort to wind up Mayor Boris or is it just that Bob Crows ego needs a boost after his parties drubbing at the Euro Elections. The strike will only anger normal Londoners and their pay demand of 5% is way over the top in the current climate they are little better than the bankers, just trying to get what they can whilst the rest of the country tightens its belt.