MEK was founded on 5 September 1965 by leftist Iranian students affiliated with the Freedom Movement of Iran to oppose the U.S.-backed Shah Mohammad Reza Pahlavi. The organization engaged in armed conflict with the Pahlavi dynasty in the 1970s and contributed to the overthrow of the Shah during the Iranian Revolution. It subsequently pursued the establishment of a democracy in Iran, particularly gaining support from Iran's middle class intelligentsia. After the fall of Pahlavi, the MEK refused to take part in the constitutional referendum of the new government, which led to Khomeini preventing Massoud Rajavi and other MEK members from running for office in the new government. This created conflicts with Ayatollah Khomeini, and, by early 1981, authorities had banned the MEK, carrying out a major "crackdown on the group's members and supporters", driving the organization underground.