EFF leader Julius Malema has warned that if a Parliamentary motion of no confidence in President Jacob Zuma succeeds, he will still try to remain in office.
He said Zuma would argue that the ANC did not tell him to go.
"Be prepared for dictatorship... but we are not scared," he told a large crowd of opposition party supporters in Mary Fitzgerald Square in Johannesburg. "If Parliament says he must leave, and he refuses to leave, we will break him out of the union buildings by force."
Opposition parties gathered at the square while the Constitutional Court was hearing the UDM's application to force Speaker Baleka Mbete to conduct the vote of no confidence in Zuma by secret ballot.
The parties were marching to court from the square.
"We are today from different political parties, joined by civil society. [The] court must hear us today that we want to protect the Constitution of our country," Malema said.
"There will never be a democratic without a secret ballot. ANC members of Parliament are being intimidated [to prevent them voting against Zuma]. We have a responsibility to defend each and every member of Parliament - we must even protect ANC members."
He said "criminals" were gathering for a march in Durban against what they believe is judicial overreach.
"They are intimidating the judiciary. They are saying judges are captured, because they think judges are like them - they get captured through a plate of curry.
"But our judges do not have the appetite for a plate of curry," Malema said in reference to the controversial Gupta family.
'Deserve to be in jail'
DA leader Mmusi Maimane told the crowd he read in the media at the weekend that Zuma said he does not know what he did wrong.
"We are here to remind Jacob Zuma of what he had done wrong. "We are here to say 'because of you nine million people don't have jobs'... It's because of you and your incapable government that we are not able to restitute land.
"We are here to say 'you deployed to Brian Molefe to Eskom'... Brian you deserve to be in jail."
He also said the people of South Africa wanted Zuma to give back to them the R200 million spent on his Nkandla homestead.
They large crowd of opposition supporters, including members held aloft "Fire Zuma" and "We are one" placards.
Some waved the national flag while singing "Zupta Must Fall".