Social Security Organization (SSO) is a social insurer organization in Iran which provides coverage of wage-earners and salaried workers as well as voluntary coverage of self-employed persons. In 1975, the Social Security Law was approved and the SSO was established. Iran did not legislate in favor of a universal social protection, but in 1996, the Center of the Statistics of Iran estimated that more than 73% of the Iranian population was covered by social security. Membership in the social security system is compulsory for all employees.