Under the UN Charter every Member must comply with ICJ decisions, and the Security Council can act if a party fails to
Background
Chapter XIV of the UN Charter makes the International Court of Justice the principal judicial organ of the United Nations. All Members are ipso facto parties to the Court's Statute. Article 94 says each Member undertakes to comply with the Court's decision in any case to which it is a party. If a party fails to perform its obligations under a judgment, the other party may have recourse to the Security Council, which may make recommendations or decide on measures to give effect to the judgment. Under Article 96, the General Assembly or the Security Council may request an advisory opinion on any legal question.
In plain words
Advisory opinion Advisory opinion — The Court's legal opinion on a question put to it by an authorised UN body, not a judgment in a dispute.