Since the Islamic Revolution of Iran in 1979, the constitution of Iran states regarding freedom of expression: "the press is free to express their opinion, unless it is against the foundation of Islam or rights of the people, and the law will explain the details". (article 24, The Constitution of Islamic Republic of Iran).
The details have been explained, not in legislation of the parliament, but in an act issued by the Supreme Council of Cultural Revolution, which names the subjects that "do not deserve to be published", for example: Renouncing the fundamentals of religion; promoting corruption; inviting the society to riot against Iran; promoting the ideas of terrorist and illegal groups and corrupted sects and defending monarchy; stimulating conflicts between the various ethnic or religious groups or creating problems in the unity of the society and the country; mocking and weakening the national pride and nationalistic spirit, and creating an atmosphere of losing national values to the culture and civilization of western or eastern colonizing systems.