Mr Sharif (l) and Mr Zardari - will they stand for parliament?
The main parties in Pakistan's new government have condemned a decision by the election commission to postpone a number of by-elections for two months.
The commission says the delay is partly due to security concerns, particularly in the north-west.
Neither of Pakistan's top politicians, Asif Ali Zardari and Nawaz Sharif, ran in the February elections that saw President Musharraf's allies routed.
Reports say both are considering standing in the by-elections.
The election commission is staffed by presidential appointees. But a spokesman for Mr Musharraf denied that the delay was politically motivated, saying that he had had no involvement in the decision.
Members of Mr Zardari's Pakistan People's Party (PPP) and Mr Sharif's Pakistan Muslim League-N said the election commission had not consulted them about the delay.
"We condemn this. This is an anti-democratic step," the PPP's Sherry Rehman said.
In a statement Mr Zardari said: "Even if the law and order situation was bad in any particular locality, it provided no justification to postpone by-elections throughout the country."
Observers say Pakistan has been relatively peaceful since militants declared a ceasefire recently.
The elections are for eight seats in the national assembly and 32 provincial assembly seats.
They have already been delayed once and were due to be held on 18 June. They have now been scheduled for 18 August.
The secretary of the election commission said it was concerned by security in North West Frontier Province.
He also said June was a bad time to hold the polls because the national and provincial assemblies would be busy with budget issues.