Employers can always chose to force annual vacation payout - or have reduced hour rollover (i.e. halved if rolled over). I absolutely despise any sort of vacation reduction (or full disappearing on expiration) but having the hours paid out is a pretty equitable situation. If I want to take a vacation in January and am forced to take it using unpaid hours (I'll always talk to managers about carrying over hours for some fixed vacation if they're willing and usually get positive feedback) then I'll at least end up neutral at the end of the year (or employment) when those accrued hours get paid out.