Exchange of accusations was running high Saturday, in a rivalry that has increasingly been portrayed by Morsi supporters as an attack on Islamists in power.
The Tamarod youth movement claimed its petition is evidence of what it says is widespread dissatisfaction with Morsi's administration, and has used the signature drive as the focal point of its call for millions of people to take to the streets to demand the president's ouster.
Mahmoud Badr, a Tamarod leader, told reporters Saturday a total of 22,134,460 Egyptians have signed the petition. He did not say whether there had been an independent audit of the signatures.
Badr blamed Morsi supporters of dragging the peaceful movement toward violence to "terrorize" the public and avert a mass turnout in the streets.
On Tamarod's Twitter account, the movement appealed to supporters to gather in every street in their hometowns instead of converging to the main rallies planned in Tahrir square and outside Morsi's palace.
At a press conference organized by Morsi supporters late Saturday for their members killed in recent violence, organizers showed multiple videos of previous protests where violence raged, showing images of attacks on the Brotherhood offices and blaming "paid thugs" for it.
"Tamarod are thugs," the crowd chanted at the conference held at the pro-Morsi sit-in.
Assem Abdel-Maged, leader of the formerly militant Gamaa Islamiya group, told the crowd that the Tamarod campaign was a "crusader war" against Islamists, led by extremist Christians to liberate Egypt from Islam. He added that his supporters collected 26 million signatures in support of Morsi.
"The issue now is war," he said. "Sunday's march is decisive."
Morsi's supporters have long doubted the validity and authenticity of the collected signatures.
"How do we trust the petitions?" asked Brotherhood member Ahmed Seif Islam Hassan al-Banna. "Who guarantees that those who signed were not paid to sign?"
But opponents of Morsi say the petition has already served its purpose, dealing a symbolic blow to Morsi's mandate and putting in stark terms the popular frustrations with an administration that critics say has failed to effectively deal with the country's pressing problems, including tenuous security, inflation, power cuts and high unemployment.
In a statement ahead of the protests, opposition leader Mohammed ElBaradei said massive turnout is expected Sunday, calling for it to be peaceful and civilized. He called on Morsi to listen to the masses, and accept early elections.
"All of Egypt should go down tomorrow to say that we want to go back again to the ballot box," ElBaradei said in his recorded message sent to reporters. "We gave (Morsi) a driving license but he couldn't drive the car."
He added: "We all feel the country is collapsing, not because the president is from the Brotherhood ... But because the ruling system has failed completely."
On Saturday, Morsi met with the defense and interior ministers to review preparations to protect the protesters and vital state facilities during Sunday's demonstrations.
The focus of Sunday's protests is Morsi's Ittihadiya palace in Cairo. As a precaution, the president and his family are reported to have moved into the Cairo headquarters of the Republican Guard, the branch of the army tasked with protecting the president and presidential palaces.
With expectations of violence running high, the military has dispatched troops backed by armored personnel carriers to reinforce military bases on the outskirts of cities expected to be flashpoints.