What it is
Under a use-it-or-lose-it rule, unused hours vanish at year end, at an anniversary date, or at separation. Some states require paying expired hours at separation because the balance was earned, not forfeited; others leave the outcome to the plan language.
What to do about it: Read the forfeiture sentence in the plan first. If separation is listed as a forfeiture event, negotiate the payout before you give notice, in writing.
Plain-language description of US practice, not legal, tax, or financial advice. The paired guide carries the citations, dates, and thresholds; the state pages carry the local windows.