Democratic Alliance (DA) leader Mmusi Maimane on Tuesday called on ruling party MPs to vote according to conscience and help to remove President Jacob Zuma from office in a vote of no confidence he called historic.

“Today is a historic day. South Africa faces a choice between corruption and a prosperous South Africa. As life is getting hard for our people, it is important that we put South Africans first,” Maimane said in a brief statement a few hours before the debate on the motion of no confidence.

“Today MPs get to exercise their vote by using a secret ballot. I want to urge all ANC [African National Congress] MPs to vote with their conscience today.

“Let us put the people of South Africa first. Let us vote to remove Jacob Zuma so that we can start moving South Africa in the right direction.”

Speaker Baleka Mbete on Monday announced that she would allow voting by secret ballot on the opposition’s seventh motion of no confidence in Zuma.

The Constitutional Court left the decision in her hands after opposition went to court in bid to force a secret ballot. After weeks of speculation about her decision, she made an announcement less than 24 hours before the start of the debate on the motion.

It needs a simple majority to succeed, meaning that 50 ANC MPs will have to vote with the opposition in order to remove Zuma from office and force the collapse of his Cabinet. The ANC holds 249 seats but two are vacant after two ruling party MPs died in recent weeks.

Four ANC MPs have said openly they will vote according to conscience – former finance and tourism ministers Pravin Gordhan and Derek Hanekom, Makhosi Khoza and Mondli Gungubele.

Mbete’s decision raises the spectre of more ANC MPs defying a three-line whip to vote against Zuma.

But one senior opposition MP said he believed some of the anti-Zuma momentum that shook the ANC after the president fired Gordhan in March had been lost, even if the secret ballot will now offer dissenting MPs protection against retribution for breaking ranks.

“It will be touch and go. We have been trying to lobby them but it may be too late. We lost too much time with the court case,” he said.

“After he fired Pravin, they were very angry. They were calling and asking to have coffee with us. Now we are calling them and they don’t answer.”

Voting will not take place electronically but by paper ballot, Parliament confirmed on Tuesday morning.