Economic sanctions would prevent the chosen colony from trading with other colonies until they comply with the demands of the rich colonies. Sanctions can't be placed on rich colonies as a reward for putting in the time and effort to grow their colony(colonies are considered rich when they reach a certain threshold). Sanctions can only be implemented by holding a vote among the rich colonies.
hmm not sure how that would work but if gifting is an issue than why not think of a colony needs to reach a certain gross economic b4 it can recive gifts or trades