The conflict between Sharia and law has been one of the fundamental challenges of the legislative system in Iran since the Constitutional era. In the Islamic Republic, this problem was partially resolved with the initiative of Imam Khomeini; in cases where it was possible to legislate, Sharia rulings were converted into law, in the area of ​​freedom, the establishment of laws in harmony with Sharia was considered without any problems, and in cases of contradiction, the determination of expediency was entrusted to the Expediency Council (Article 112 of the Constitution). The main question of this research is that if a law such as the “Law on Supporting the Family through Promoting a Culture of Chastity and Hijab” is Sharia-compliant but is contrary to expediency and socially unacceptable in the public sphere and in the minds of the majority of people, what institution has the authority to determine expediency? The main finding of the article is that under these assumptions, due to the inadequacy of Article 112, no institution has the authority to assess expediency and establish a secondary title, and the only efficient mechanism is to utilize Article 59 of the Constitution and refer to a referendum if the necessary conditions exist. In this way, "public opinion" will act as a complementary institution for determining expediency in socio-cultural affairs. This research was conducted using a descriptive-analytical method and based on jurisprudential, legal, and historical sources.