The Supreme Court in Pakistan has struck down a new law designed to exempt top government officials from contempt of court charges.
Five judges, headed by Chief Justice Iftikhar Mohammed Chaudhry, said granting immunity to public office holders was unconstitutional.
The ruling could see Prime Minister Raja Pervez Ashraf thrown out of office.
His predecessor Yousuf Raza Gilani was removed by the court in June, after he was convicted of contempt.
The BBC says the ruling puts the Supreme Court on a collision course with the government once again.
The court wants the government to ask Switzerland to reopen an old corruption case against President Asif Ali Zardari.
Mr Gilani refused, arguing that the president had immunity from prosecution as head of state.
The court has given Mr Ashraf until 8 August to write to Switzerland. If he fails to do so, correspondents say he could face the same fate as Mr Gilani.
The BBC reports the corruption case dates back to the 1990s when Mr Zardari and his late wife, former Prime Minister Benazir Bhutto, were accused of laundering kickbacks in Swiss bank accounts. Mr Zardari says the charges are politically motivated.