Make it illegal to sack or punish someone for refusing to change their contract. Varying contract terms without agreement should be classed as unfair dismissal.
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Loyal long serving staff are having their benefits removed, such as guaranteed working hours, paid breaks, paid bank holidays, things they've worked hard for, for years, now are being treat like they're worthless.
It is unfair to force a contract change. Contracts of employment should be legally binding and honoured for the length of your service.