"Democratic life cannot start with an unhealthy law," Aoun said in an interview to AFP on Wednesday.
The forthcoming parliamentary elections would be "flawed due to legal falsification", he said.
Christians have charged the law is unfair because it allows only 15 Christian MPs to be elected by Christian voters, while 49 others would be elected by Muslims, and is therefore not representative of their community.
Parliament has an equal number of seats reserved for Christians and Muslims.
Aoun said the opposition was falling apart in the run-up to phased elections, which are due to start on 29 May, a month after Syria completed a 29-year troop deployment.
"This so-called opposition was only seasonal. Its representatives were in power" during the period when Syria dominated Lebanese politics, said the general, who returned on 7 May from 15 years of exile in France.
Former Sunni Muslim prime minister Rafik al-Hariri and Druze leader Walid Jumblatt took part in several pro-Syrian governments, apart from 1998-2000, and only broke away to join the opposition ranks in September 2004.
Aoun: The opposition has failed
to drawn up a common platform
Aoun charged the opposition with failing to draw up a common platform to contest the polls, to be held over four consecutive Sundays until June 19.
He accused Jumblatt and Saad al-Hariri, who has taken the mantle of his father - officially his allies - of bowing to international pressure to accept the polls "under whatever conditions".
Aoun said other opposition members had agreed "to self-destruct and destroy the hope for change", but he did not close the door on cooperation and said he was ready to try to draw up a common programme "up until the last minute".
"The priority is to hold fair elections and not the date. But for the decision-makers, it's the form that counts. Nothing has changed. Even if the Syrians have gone, their methods remain," he said.
Along with Hariri and Jumblatt, some Christian opposition figures also deferred to demands from Paris, Washington and Riyadh not to delay the elections and risk instability and a power vacuum in the wake of Syria's departure.