Pakistan's top court has initiated contempt proceedings against the prime minister for failing to carry out the court's order to open a corruption probe into the president.
The Supreme Court ruling against Prime Minister Yousuf Raza Gilani means he could be prosecuted, leading to his dismissal.
The court ordered Mr Gilani to appear before the court on Thursday to explain why he has not complied with the order.
Judges are ordering the government to open a corruption probe into President Asif Ali Zardari dating back to the 1990s.
The government has refused, saying Mr Zardari has immunity.
The court order is the latest development in an ongoing political crisis in Pakistan that pits the civilian government against the army, which has three times seized power in a coup.
Many observers say the spike in tensions between those two cannot be separated from the manoeuvring of the Supreme Court, which has sanctioned past coups.
The fault line in the country is the same one that has plagued Pakistan since its creation in 1947: an army that cannot stomach taking orders from elected politicians, and which has three times seized power in coups.
The government has given the generals control over foreign and security policy, but the civilian leadership and the top brass have never seen eye-to-eye since Mr Zardari and Mr Gilani took office in 2008.
Confrontation between the army and the government broke out last week over an unsigned memo delivered to Washington last year offering the US a raft of favourable security policies in exchange for its help in thwarting a supposed army coup.
The Supreme Court formed a commission to investigate the affair. Mr Gilani criticised the army for co-operating with the probe, and has said the stand-off is nothing less than a choice between "democracy and dictatorship".
Mr Gilani's comments followed a warning from the generals - who were infuriated by the memo - of possible "grievous consequences" ahead.