Pakistan's Supreme Court is set to hear challenges to several constitutional measures which parliament passed in April.
The constitutional amendments bill received overwhelming support in both upper and lower houses of parliament.
Measures included transferring key powers from the office of president to the prime minister.
The court is due to reconsider decisions such as granting parliament the power to appoint top judges.
It is also set to review the National Reconciliation Ordinance (NRO) - a piece of legislation passed by former President Pervez Musharraf, which effectively granted senior politicians and others amnesty from corruption charges.
In December the court struck down the amnesty, meaning that President Asif Ali Zardari could face challenges to his rule.
There are still court cases pending in Pakistan against Mr Zardari who spent years in jail on corruption charges he says were politically motivated.
His office currently provides him with immunity from prosecution.
But reports say the court has now ordered Pakistan's government to approach the Swiss government to revive money-laundering cases against President Zardari, which had earlier been withdrawn under the NRO.
On Tuesday Law Minister Babar Awan is set to appear in court to defend the government's position on the issue.
The BBC's M Ilyas Khan in Islamabad says there is evidence that the Supreme Court's increasing interference in the affairs of the executive is beginning to concern some of the most prominent leaders of the lawyers' movement.
Many supported Chief Justice Iftikhar Chaudhry in his long battle with the previous government.
Our correspondent points out that a key leader of that movement, Aitezaz Ahsan, recently commented that if 17 judges strike down a parliamentary amendment which has the force of 170 million people behind it, a clash of institutions cannot be avoided.
But Pakistani Prime Minister Yousuf Raza Gilani says he has assured the Supreme Court that the government will abide by its decisions and that no confrontation would be allowed to flare up.