Coercively is the adverb: doing something by threats or orders, not by asking. You will almost never hear it in daily conversation. It belongs in careful writing: a rule may be applied coercively, or a person may act coercively. Even in writing, many people prefer a clearer phrase such as "by force" or "under threat," because coercively is a long, cold word and readers may stumble. The meaning is the same as coercive, only it tells you how something is done.