The country's third largest party, the Economic Freedom Fighters (EFF), has called for a "national shutdown" next Monday, March 20..
EFF is demanding Ramaphosa's resignation for his handling of South Africa's sickly economy, electricity shortages and stratospheric unemployment.
Speaking at a news conference in Pretoria during a state visit by Tanzanian President Samia Suluhu Hassan, Ramaphosa declared "disorder and anarchy will not be allowed."
The military will be on standby for reinforcement if needed.
If protestors "restrict the rights" of other citizens "and unleash violence, our security forces are going to defend the people of South Africa," he said.
Ramaphosa noted the protests were scheduled to take place a year before general elections.
The timing, he charged, revealed that political parties are "positioning themselves because they want to win the vote."
EFF leader Julius Malema told reporters on Wednesday "we have to shut down this country to show the whole world that we are concerned about the state of affairs."
His party has called on South Africans to avoid going to work and school or operating business on the strike day.
Ports, parliament, border crossings and the Johannesburg stock exchange building among others will be targeted as key protesting points, Malema said.
Separately, Police Minister Bheki Cele said Thursday that officers will be "out in their numbers" to protect citizens who wished to work, conduct business or travel.
Some businesses and schools have voiced concern about operating on the protest day, and some have already opted to pull down their shutters.
"We expect there will be full order and harmony," said Ramaphosa.
Once championed as a graft-busting savior after the tainted era of his former boss Jacob Zuma, Ramaphosa is struggling to hold on to power.
He narrowly escaped a parliamentary vote in December that could have initiated impeachment proceedings against him over half-a-million dollars in undeclared cash hidden at his farm.
He holds the presidency thanks to a majority in parliament by the African National Congress (ANC), which led the fight against apartheid and has ruled since the advent of democracy in 1994.
But the ANC's popularity has eroded as the country's problems have multiplied, and Ramaphosa's position is in doubt.
"Regime change can only come about through the vote, it cannot come about through anarchy," Ramaphosa said.