Mr Sharif wants to re-enter parliament
Pakistan's supreme court has ordered the postponement of a parliamentary by-election that former PM Nawaz Sharif was banned from contesting.
It said that Thursday's vote should not be held until it had decided on a government appeal against Mr Sharif's disqualification from the Lahore poll.
A panel of three judges in Islamabad said that it would not deliberate on the issue until 30 June.
The government filed an urgent appeal challenging the ban on Wednesday.
It argued that election disputes should be heard by an election tribunal and not the courts, which it said had no jurisdiction in such matters.
Mr Sharif was barred from running in elections in February because of convictions relating to the 1999 coup in which he was toppled.
He wanted the ban lifted in time to run in Thursday's by-election, but on Monday the Lahore high court upheld the earlier ruling.
Prime Minister Yousuf Raza Gilani told parliament the government was appealing because Mr Sharif was a key partner in the governing coalition.
Mr Sharif (l) and Mr Zardari have been at loggerheads over the judges issue
"We have filed a petition in the supreme court on behalf of the federation, challenging the Lahore high court decision to bar Nawaz Sharif from contesting the by-election," deputy Attorney General Raja Abdur Rehman told the AFP news agency on Wednesday.
"Our plea is that under... the Pakistani constitution, election disputes should be heard by election tribunal and not the high court. High courts have no jurisdiction to hear such cases."
Correspondents say Monday's ruling was a major political setback for Mr Sharif in his efforts to re-enter parliament.
His Pakistan Muslim League-Nawaz (PML-N) dismissed the ruling as "politically motivated", saying the judges who made it had been appointed by his rival, President Pervez Musharraf.
Mr Sharif has been demanding the immediate reinstatement of judges sacked by President Musharraf during a state of emergency last November.
Mr Sharif was deposed as prime minister by Gen Musharraf in a 1999 coup and later sent into exile, but has re-emerged as a major force in Pakistani politics.
His PML-N was the second largest party in the general elections in February that saw President Musharraf's allies routed.
Correspondents say the Lahore court's decision has exacerbated tensions between the PML-N and the main party in the governing coalition, the Pakistan People's Party (PPP).
The BBC's Barbara Plett says Mr Sharif's party joined the coalition government with the expectation that its leader was now clear to run for office.
Since then, though, the coalition has foundered, and the court's decision may further strain the fragile, anti-Musharraf alliance, our correspondent says.