I worked for one company where, as soon as the old earned time-off balances were wiped away, management of the biggest engineering group started telling people

I worked for one company where, as soon as the old earned time-off balances were wiped away, management of the biggest engineering group started telling people they couldn't take more than 4 weeks off. Sure, it was 3 weeks before the change, but you could roll it over, or be paid for it if you left.