The law mandates that the schools, which are attended by millions of students, close by Sept. 15, 2015, the BBC reported Saturday.
The schools, which prepare students for entrance examinations to win limited spots at state secondary schools and universities, are a major source of income for Gulen's Hizmet movement.
Meanwhile, at a rally held Friday, Turkish Prime Minister Recep Tayyip Erdogan called anti-corruption and graft protesters "atheists and terrorists," the Hurriyet Daily News reported.
"We opened a boulevard in Ankara on Monday [Feb. 24] despite the [protests of] leftists, despite those atheists. They are terrorists, but the [main opposition Republican People's Party] CHP is calling them 'our youth,'" Erdogan said.
Erdogan also criticized Gulen, who has been living in self-imposed exile in the United States for the past 15 years, for not allowing girls at his schools to wear headscarves.
"He [Gulen] was saying you may not wear headscarves. Why do you [Gulen] get involved? Because he does not have any children," he said.
The prime minister said people not to send their children to private prep schools.