Women without veils complained they were not allowed to vote for the new Egyptian anti-secular constitution. Mass protests on Tuesday.
Egypt's opposition is calling for mass protests on Tuesday over alleged polling violations after Islamists backing Muslim Brotherhood President Mohamed Morsi claimed victory in the first round of a referendum on a new charter.
Thousands of women complained they were not allowed to vote because they were not veiled, and Christian women also said they were turned away.
A low one-third turnout fueled charges of forged ballots, campaigning inside polling stations and judges being replaced by civilians favoring the Muslim Brotherhood.
A group of top judges announced on Monday it would boycott supervision of the second round, and Germany said it has postponed debt relief for Egypt because of concerns over the country's commitment to democracy.
Adding to the complications for Morsi, the prosecutor general named by the president as he temporarily assumed sweeping powers last month handed in his resignation, a judicial source told AFP.
The opposition coalition, the National Salvation Front, urged Egyptians to "take to the streets on Tuesday to defend their freedoms, prevent fraud and reject the draft constitution" ahead of the second round.
It claimed "irregularities and violations" marred the initial stage of the referendum last weekend across half of Egypt that Morsi's Muslim Brotherhood said resulted in a 57 percent "yes" vote, according to its unofficial tally.
On the legal front, the State Council Judges Club, whose members took part in overseeing the first round as required by law, said it would boycott next Saturday's vote because the authorities had failed to live up to their promises.
The association has demanded that a "siege" of the Supreme Constitutional Court by Brotherhood supporters be lifted. But the action has continued without any intervention by the authorities, it said.
In Germany, a spokesman for the overseas development ministry said a plan to forgive up to 240 million euros ($316 million) of Cairo's debt had been delayed indefinitely.
Germany's Development Minister Dirk Niebel said earlier he had serious reservations. "There is the danger that the dictatorial system of ousted president (Hosni) Mubarak is returning," he told the daily Berliner Zeitung.
Large protests both for and against the proposed constitution have been staged during the past three weeks, sparking violent clashes and revealing deep divisions in society over Morsi's rule.
Early this month, eight people were killed and more than 600 hurt when rival protesters fought outside the presidential palace in Cairo.
The opposition says the constitution weakens human rights, especially those of women, and undermines the independence of judges while strengthening the military.
It fears Islamists propelled into power after a revolution last year that toppled Mubarak's 30-year regime want to establish Sharia-style laws.