Egypt's first democratic elections since the overthrow of Hosni Mubarak have been called into question after an electoral coalition led by the Muslim Brotherhood threatened a boycott.
The coalition said in a statement it would not take part in November's legislative elections if a controversial article in the new electoral law was not amended.
The bloc objected to Article Five of the electoral law, which bans political parties from running in a third of the seats in parliament, which are reserved for independent candidates.
"We refuse to take part in elections if Article Five of the electoral law is not cancelled," said the statement, issued late Wednesday.
The statement was published in the name of the Democratic Coalition which, as well as the Muslim Brotherhood, includes the Freedom and Justice Party, an offshoot of the Brotherhood, and the liberal al-Waf party.
Egypt's interim military rulers -- the Supreme Council of the Armed Forces (SCAF) -- announced on Tuesday that the first stage of parliamentary elections would be held on November 28.
But in an amendment to the electoral law, it said two-thirds of parliament would be elected through a party list under the proportional representation system.
The rest would be elected through a simple majority -- but only independent candidates would be eligible to run for them.
But the statement from the Democratic Coalition said they were "astonished" at the SCAF's position.
They had, it argued, "refused the request of the political forces to elect all members of parliament by the closed, proportional lists system".
Under Article Five, it argued, a third of the seats would be exclusively for "independents and candidates from the old regime", it added.
The Democratic Coalition is not alone in objecting to this part of the electoral law.
More than two dozen political parties have already rejected it, objecting that it could help return old regime figures to parliament.
They have called for a pure proportional representation system and the activation of a law that would ban corrupt politicians from running for office.
Under the old system, hundreds of candidates ran as independents if they did not make on to Mubarak's National Democratic Party lists, only to join the party after winning seats.
But Article Five of the new electoral law specifically forbids those elected as independents from joining a parliamentary bloc once elected -- on pain of losing their seats.