If they are illegal I'm sure they will. If they're not, well, what would you suggest they do? What would you suggest they can do? Wail that "It's not fair"? Lobbying just doesn't work with a hardball company like EJ.
And if these guys are employed by an agency and not EJ then EJ-BALPA can do precisely NOTHING for them in any situation as they do not and can not represent them. BALPA itself could, if the contract is illegal, but that would require the flexicrew guys themselves to organise a campaign with BALPA head office direct. Do you see that as a likely outcome? I doubt the company is losing any sleep over the possibility of that.