Pakistani state TV has said that the country's Supreme Court has struck down a law recently passed by parliament and aimed at protecting the prime minister from being charged with contempt of court.
The report said the court on Friday declared the law unconstitutional.
Pakistan's parliament passed the law in July after the court convicted former Prime Minister Yousuf Raza Gilani of contempt and ousted him from office for failing to reopen an old corruption case against President Asif Ali Zardari.
The aim of the law was to prevent the new premier, Raja Pervaiz Ashraf, from suffering the same fate.
The court has demanded Mr Ashraf write a letter to Swiss authorities asking them to reopen the old graft case and has set an August 8 deadline for the government to respond.