It seems to me that if managements unilaterally change a contract without negotiating those changes then that voids the contract. Thus the pilot group would be within their rights to strike or take such action that would force management to bargain in good faith.
I find it ironic that most of the support for the strike in this thread comes from those outside europe, whereas those within europe, home to the wildcat strike, are indignant over the prospect of a pilot group standing up to a management that sees fit to change their contract without negotiating. What would the French do?