Media advisor of the Muslim Brotherhood's Freedom and Justice Party Mourad Aly has said that he welcomes Tuesday's demonstrations as long as they remain peaceful.
Opposition forces have organized a "Last Warning" march to Egypt's presidential palace on Tuesday against a presidential decree and a draft constitution.
Egyptian President Mohamed Mursi issued a constitutional decree on November 22 expanding his powers while an Islamist-dominated assembly finished drafting a new charter on Friday allowing it to be put to a referendum on December 15.
"We staged demonstrations on Saturday where millions rallied without one case of sexual harassment, attacks or vandalism or disruption of public order", Aly said.
He held leading opposition figures, including Mohamed ElBaradei and Hamdeen Sabahi, responsible for any violence that may happen on Tuesday.