Move comes as PM Gilani appears before supreme court in contempt hearing for not pursuing fraud case against president.
Pakistan's President Asif Ali Zardari risks losing his immunity from prosecution, the Supreme Court has said in a contempt hearing against Prime Minister Yusuf Raza Gilani.
Gilani appeared in court on Thursday, facing contempt of court proceedings for failing to pursue corruption cases against the president.
Gilani had been summoned to explain his refusal to ask Switzerland to re-open fraud cases against Zardari.
The prime minister told the court that Zardari cannot be prosecuted as he enjoys immunity.
"It is my conviction that he has complete immunity inside and outside the country," Gilani told judges. "In the constitution, there is complete immunity for the president. There is no doubt about that."
However, Al Jazeera's Imtiaz Tayeb, reporting from the hearing, said the court then challenged the president's alleged immunity.
"The court dropped a bit of a bombshell, that what if they don't recognise the immunity that is purportedly under the constitution?," he said.
"The prime minister's lawyer then suddenly started with a different defence, saying it's not the president's immunity that is questioned or that he'll fight about, but that he'll fight about whether the issue is whether the prime minister believed the president had immunity."
Hundreds of policemen were stationed outside the court in the heavily protected constitutional sector of Islamabad.
Several senior cabinet ministers and leaders of allied political parties attended the proceedings.
The next court hearing was set to February 1, and the court said the prime minister's legal representation could attend the session on his behalf.
In 2008, Swiss authorities shelved a probe into alleged money laundering by Zardari and his late wife, Prime Minister Benazir Bhutto, who was assassinated in 2007.
The couple were suspected of using Swiss bank accounts to launder about $2m in alleged bribes paid by companies seeking customs inspection contracts in Pakistan in the 1990s.
A Swiss prosecutor has since said it would be "impossible" to reopen the case against Zardari since he benefits from immunity as a head of state.
The statute of limitations of the case expires in April.
The summoning of Gilani has plunged his government deeper into a crisis that could force early elections within months.
The government is also under immense pressure from the army and judiciary over an unsigned memo asking the US to prevent a feared coup last May.
Supreme Court judges have six options on how to proceed which include finding Gilani in contempt, disqualifying the prime minister and president, and holding early elections.
Analysts say Gilani has to either resign or find a way of satisfying the court order if he wants to keep his job.
Some have suggested that the ruling Pakistan People's Party (PPP) could sacrifice Gilani to protect the president, who has been accused over the controversial memo that sought US assistance to curb the powerful military.
However, other observers have suggested that the court's real target is Zardari.
During the 1990s, Zardari had multiple cases of corruption and even murder lodged against him, all of which he says are false and politically motivated.
An amnesty deal that protected him from prosecution was nullified in 2009 and the court has been pushing for the government to re-open and investigate the corruption cases against Zardari.