Pakistan's Supreme Court on Monday began hearing a raft of crucial petitions against General Pervez Musharraf's plan to be re-elected as president while holding the post of army chief.
The legal challenges come just days before military ruler Musharraf is expected to file his nomination papers for a parliamentary ballot for another five-year term in office, a vote that is due before October 15.
The petitions have been filed by the country's leading fundamentalist party, Jamaat-e-Islami, the outspoken cricketer-turned-politician Imran Khan and an association of pro-democracy lawyers.
Musharraf has been beset by crises since his botched attempt in March to sack Supreme Court Chief Justice Iftikhar Muhammad Chaudhry, which sparked nationwide protests and a spate of judicial activism.
"Musharraf has never been the duly elected president," Akram Sheikh, the counsel for the Jamaat-e-Islami party, told the court as his opened his arguments.
The judges are expected to rule by the end of this week.
The appeals all argue that Musharraf, who seized power in a bloodless coup in 1999, should not be allowed to hold his military and civilian offices at the same time.
They also oppose Musharraf's aim to be re-elected by the outgoing parliament and provincial assemblies, saying there should be a general election first to reflect the changing political landscape.
Sheikh said a law introduced in 2004 allowing Musharraf to stay on as president-in-uniform was "discriminatory and should be struck down by the court."
Former commando Musharraf's plans for re-election have been the sticking point in negotiations with self-exiled former prime minister Benazir Bhutto on a power-sharing pact.
Bhutto, who has been living in Dubai and London to avoid corruption charges in her homeland, announced on Friday that she intends to return to Pakistan on October 18, with or without a deal.
Pakistani authorities a week ago expelled another ex-premier, Nawaz Sharif, when he tried to fly home to challenge Musharraf, the man who ousted him eight years ago.
As the political scene in the nuclear-armed Islamic republic of 160 million people hotted up, the opposition condemned "unconstitutional" changes in election rules that previously barred Musharraf from seeking a new term.