All praise be to Allaah Alone, and peace and blessings be upon the Messenger of Allah, his family and Companions.
To proceed: We have received a question from some Pakistani Muslims that can be summarized as follows:
What is the ruling on those who call for application of socialist and communist principles and fight the rulings of Islaam? What is the ruling on a person who helps such people in their demands, scorns those who call for the application of Sharee`ah (Islaamic law), speaks ill of them and slanders them? Is it permissible to allow those people to be Imaams and preachers in Masjids (mosques)?
Answer: All praise be to Allaah, and peace and blessings be upon the Messenger of Allaah, his family, his Companions, and those who follow his guidance. There can be no doubt that Muslim rulers must judge according to Sharee`ah in all affairs. Moreover, they have to fight any other laws that oppose Sharee`ah. This is indisputable and unanimously agreed upon by all Muslim scholars. There are many pieces of evidence on this from the Glorious Qur’aan and the Prophetic Sunnah that are known by scholars, including the Aayah (Qur’aanic verse)… read more here.