The new rules approved Friday ban billboard owners from giving discounts to most political parties, subject to heavy fines. The government says the aim of the law is to fight illegal party financing.
The law is seen aimed mainly at the far-right Jobbik party whose current, widespread billboard campaign says Prime Minister Viktor Orban and his allies are stealing while other Hungarians have to work for their money.
The billboards are in spaces rented from Lajos Simicska, a businessman and former head of Hungary's tax office who accumulated his fortune mostly through state construction projects while he was close ally of Orban. They had a falling out in early 2015.