Pakistan's main opposition party demanded Sunday that the president immediately relinquish much of his power amid calls for the unpopular leader to assume a ceremonial role or resign.
The political turmoil threatens to distract the U.S.-allied country from its fight against the Taliban and al-Qaida near the Afghan border.
President Asif Ali Zardari inherited sweeping presidential powers from his predecessor, Gen. Pervez Musharraf, who staged a 1999 military coup and resigned last year. Zardari has promised to give them to the prime minister, in line with Pakistan's original constitution, but has been accused of foot-dragging by an angry opposition.
His position has been further weakened by the expiration of an amnesty protecting him and several key allies from graft prosecution, raising the possibility of legal challenges to his rule in the coming months.
On Friday, Zardari transferred command of the country's nuclear arsenal to the prime minister and promised to surrender other key powers — chiefly the authority to fire an elected government and appoint top military chiefs — by the end of the year.
Shahbaz Sharif, the brother of main opposition leader Nawaz Sharif and chief minister of Pakistan's largest province, Punjab, said Zardari has made similar promises to abolish the measure known as the 17th constitutional amendment and needs to act now.
"I would ask the president to immediately abolish the 17th amendment," Sharif said to reporters in Lahore. "The nation would appreciate this act."
The upheaval comes as President Barack Obama's administration is expected to announce this week a new strategy for defeating the Taliban in neighboring Afghanistan and on Pakistan's northwestern border. The United States needs political stability in Pakistan to have any hope of succeeding.
Coup, ouster look unlikely
A military coup to oust Zardari appears unlikely, as does impeachment, since he heads the largest party in Parliament.
Some have demanded his resignation, but the opposition has not called for anti-government street rallies, perhaps wary of pushing the country into chaos and paving the way for more military rule.
Zardari, 54, is languishing in opinion polls just 15 months after taking office. He has long been haunted by corruption allegations dating back to governments led by his late wife, Benazir Bhutto. He denies any wrongdoing.
He also has found himself locked in a power struggle with the powerful military, which has objected to his overtures toward nuclear-armed rival India and his acceptance of a multibillion dollar U.S. aid bill that came with conditions some fear impose controls over the army.