"This is a power struggle and an insult to the law," Ali, a labour lawyer and leftist activist, declared on Twitter. "Don't preach about the application of the law only when revolutionaries are in jail and those who killed the martyrs go unpunished."

The Nasserist Sabbahi, for his part, who came in third in the first-round presidential vote, echoed this sentiment, describing Morsi's decree as "a waste of legal authority."

Sabbahi went on to urge Egypt's High Constitutional Court (HCC) to provide a rationale for its ruling last month declaring a parliamentary elections law – which governed last year's legislative polls – to be unconstitutional, so as to eliminate any confusion in this regard.

Moderate Islamist Abul-Fotouh, meanwhile, called Morsi's decree "unconstitutional," saying it would "open the doors to breaking the state of law."

Abul-Fotouh declared on Twitter that the only way to ensure both respect for the court ruling and the will of the people was "to call for speedy parliamentary elections."

In an unexpected show of his newfound executive authority on Sunday, Morsi issued a decree calling for the restoration of the People's Assembly. In mid-June, Egypt's then-ruling military council ordered the dissolution of parliament's lower house based on the earlier HCC ruling.