South Africa's top court is debating whether legislators can cast secret ballots in a no-confidence vote in President Jacob Zuma as hundreds protest in Johannesburg demanding his removal.

Zuma, who has been implicated in a series of corruption scandals, has survived similar votes in the parliament the past.

Baleka Mbete, parliament speaker and a senior official of Zuma's African National Congress (ANC), said she had no powers to agree to a secret ballot.

The ANC holds a majority in parliament.

The opposition believes the latest motion will have better prospects if it is conducted in secret.

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Dali Mpofu, a lawyer representing the opposition United Democratic Movement party, told the Constitutional Court in televised proceedings that the speaker had an "obligation to arrange for a private ballot".

Richard Calland, a member of the Council for the Advancement of the South African Constitution (CASAC), told Al Jazeera the opposition was lobbying for a secret ballot because ANC legislators were under pressure to vote in Zuma's favour.

"They [the opposition] believe, as do many of us, that some of the back bench men of the ANC would not be able to exercise a free will when voting on this matter because they all fear for their jobs, fear for their future," he said.

"Therefore, the secret ballot is necessary to protect them and the constitution."

Thousands of South Africans have staged protests in recent weeks demanding Zuma's resignation, and opposition parties, religious groups and civil society activists have joined forces against him.

The protests began when Zuma dismissed Pravin Gordhan, his widely respected finance minister.

The dismissal led to a sharp fall of the country's currency and stock markets, causing losses worth millions of dollars.

Mmusi Maimane, leader of the main opposition Democratic Alliance (DA) party, has appealed to ANC legislators to "vote with their conscience".

"ANC members of parliament will have to choose between what is best for themselves and what is best for South Africa," he told protesters gathered outside the Constitutional Court on Monday.

"They did not swear [their oath of office] to be faithful to Jacob Zuma, or to the ANC ... . They promised to be faithful to South Africa."

'Gap in the rules'

The constitution calls for a secret ballot to elect the president, but it is silent on the procedure for a no-confidence motion, according to Calland, the CASAC member.

"There's a gap in the rules. There's a gap in the constitution ... . And that's why the matter has ended up in court," he said.

The ANC was led by Nelson Mandela to power in the 1994 post-apartheid elections.

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However, the party has lost popularity under Zuma in the face of a number of candals and a failure to address slow economic growth, high unemployment and glaring income disparities

South Africa's Constitutional Court last year found Zuma guilty of violating the constitution after he refused to repay taxpayer money used to refurbish his private rural home.

He is also fighting a court order that could reinstate almost 800 corruption charges against him over a multi-billion dollar arms deal in the 1990s.