An employer can change its employment policy "at will" -- at any time, for any reason, or for no reason at all. However, to impose the policy on an employee, the employee must have notice of the policy change before, the employee continues working under that policy.
So, if your husband can prove that he never received any notice of the policy change before exercising the vacation benefits, then he can enforce the original policy against the employer.
Hope this helps.
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