The Council of Guardians is a gatekeeper: next to the supreme leader, it decides who may run for president, parliament or the Assembly of Experts, and it decides whether to hold referendums, and on what matters, essentially nullifying the democratic aspects of those three, popularly elected institutions. (See Article 99 of the Iranian Constitution.)
According to the Iranian Constitution, the Council of Guardians is charged with examining all legislation passed by the parliament within 10 days to ensure that it conforms to Islamic and constitutional law. The six clerics on the council judge new laws' compatibility with Islamic law. All 12 members judge new laws' compatibility with the constitution. Thus, it is the Guardian Council, not Iran's Supreme Court or its head of the judiciary, that holds the power of interpreting the constitution and of judicial review. According to Article 91, the Council of Guardians consists of twelve members; six of them must be "just and pious" clergymen who are chosen by the faqih or the Leadership Council. The other six must be Muslim lawyers who are first selected by the High Council of Justice, then approved by a majority vote of the Majlis. The members of the Council of Guardians serve six-year terms, with half the members being changed every three years.
In its first two years, the Council of Guardians did not challenge parliamentary bills and generally played a passive role in the political process. In May 1982, however, the council vetoed a law to nationalize all foreign trade and has since refused to ratify several pieces of legislation that would restrict property rights.