Bonuses can be configured to take away income instead of give it. This can be configured directly into the map by the map designer, or a game creator can override a bonus to be worth a negative amount.
While this is against the original idea behind bonuses, some map creators use this strategy to create areas that players should try to avoid.
The blockade card, gift card, or abandon card can be used give away territories to try to avoid controlling the negative bonus. However, if these cards are not available, the only way to lose the bonus is for another player to attack it.