Egypt's constitutional court has rejected five articles of a draft election law and sent the text back to the country's temporary legislature for redrafting.
The ruling may delay a parliamentary poll due in April.
"The court has returned the draft parliamentary electoral law to the Shura Council after making five observations on five articles which it found unconstitutional," a court statement said.
It did not immediately disclose which parts of the law had been censured, but the court said it would issue a fuller statement later in the day.
A source in President Mohammed Mursi's office said before the decision that if the court found fault with the law, it could delay passage of the law, and hence the election, by a couple of weeks, but probably not months.
Mr Mursi had been expected to promulgate the electoral law by 25 February and set a date two months later for voting, probably in more than one stage for different regions because of a shortage of judicial poll supervisors.
The constitutional court, made up partly of judges from ousted former President Hosni Mubarak's era, has intervened repeatedly in the transition, dissolving the Islamist-dominated parliament elected after the 2011 pro-democracy uprising.
Its composition was changed by the new constitution passed by a referendum in December.
Mr Mursi was criticised in October for issuing a decree giving himself powers to override the judiciary.
He backed down and dropped the decree weeks later following widespread protests.