A coalition of Morsi supporters said Sunday its demonstrations would be "stronger than police bullets," but also condemned the trial as a farce and an illegal assault on a freely elected president.
"What is happening now is a flagrant breach of all standards, laws and norms," the National Alliance to Support Legitimacy said in an Internet statement.
The organization demanded that Egypt's interim government not broadcast the trial.
Morsi and 14 senior Islamists and members of the Muslim Brotherhood face charges of inciting violence in the streets, which Ahram Online said could land them in prison for life.
The Muslim Brotherhood and its supporters have accused the powerful Egyptian military of staging a coup to overthrow Morsi one year after the toppling of President Hosni Mubarak. The military has said it moved against Morsi in response to widespread public anger over what it called his divisive rule.