Noncompliance can be appealed to the U.N. Security Council, which may either make recommendations or authorize other measures by which the judgment shall be enforced. Recommendations made by the Security Council are not binding on a noncomplying party. Decisions are binding, and can lead to enforcement measures should a party fail to comply. A decision by the Security Council to enforce compliance with a judgment rendered by the court is subject to the veto power of permanent members and thus depends on the members' willingness not only to resort to enforcement measures but also to support the original judgment. A rule must derive from one of these three sources in order to be considered international law.
States follow such a practice out of a sense of legal obligation.
Rules or principles must be accepted by the states as legally binding in order to be considered rules of international law. Thus, the mere fact that a custom is widely followed does not make it a rule of international law. States must also view it as obligatory to follow the custom, and not believe that they are free to depart from it whenever they choose or to observe it only as a matter of courtesy or moral obligation. This requirement is referred to as opinio juris. Some criticism against customary international law is directed at its subjective character and its inconsistency.