The NAP contract is being dealt with by the Italian union (or attempting to) but AMS for example is a new contract applicable in Holland.
The only thing BALPA can honestly do is tell its British members not to sign up for a transfer, and EZY pilots can only follow this advice. The rest is actually down to the local unions in Holland and those DEP's who end up applying for the positions not filled internally.
This might be a 'horse & cart' or 'chicken & egg' situation. I have difficulty deciding which to use. To join the Dutch VNV you might need to be operating for a Dutch company and then join the union. So to operate for ez AMS you need to accept the contract then you can join the union to complain about it. Or are you saying that the VNV could argue against the contract BEFORE it has any members employed on said contract: or can prospective pilots join VNV before being employed?