A growing number of opposition figures say they will boycott Egypt's first contested presidential elections.
Rifat Said is the latest to deal a blow to contested presidential polls
They include the leftist Tagammu party leader Rifat Said and prominent rights activist Saad Eddin Ibrahim. Other parties are expected to follow suit.
Voting will be on 7 September, which opponents say leaves little time to mount an effective campaign.
Opposition groups also say conditions will rule out any serious challenge to four-term President Hosni Mubarak.
"We had asked for radical changes to the constitution allowing for anyone to take part in the election, but the changes made do not allow for real competition," Mr Said said at a news conference.
Correspondents say the pan-Arab Nasserist and the liberal Wafd parties are all likely to announce their boycotts in the coming days.
The most serious challenger to Mr Mubarak is expected to be Ayman Nur, who heads the Ghad party.
The only other hopeful who has declared an intention to run is Talat Sadat, nephew of the late previous president, who is thought to enjoy limited support.