A vote of no confidence on South African President Jacob Zuma will be held by secret ballot, the parliament speaker announced, in a move that could encourage some ruling party parliament members to vote to oust him.

"I ... determine that voting on the motion of no confidence in the president on the 8th of August 2017 will be by secret ballot," parliamentary Speaker Baleka Mbete announced on Monday.

The vote, scheduled for Tuesday, has become a test of African National Congress (ANC) unity as senior party figures have increasingly become critical of their leader.

The president, who came to power in 2009, has been implicated in multiple corruption scandals, while the country's economy has fallen into recession and unemployment has risen to record levels.

The 75-year-old is due to step down as head of the ANC in December, and as president before the 2019 general election - lessening pressure for his party to seek imminent change.

The Speaker's decision has been subject to a long legal battle waged by opposition parties, with the Constitutional Court ruling that a secret ballot was permissible.

The main opposition Democratic Alliance (DA) party said the vote was "an opportunity for us all to stand up to corruption and get rid of President Zuma and his cabinet".

Musi Maimane, DA's leader, urged ANC lawmakers to vote Zuma out.

"ANC MPs now have no excuse," he said.

Al Jazeera's Haru Mutasa, reporting from Cape Town, reported that the opposition needs at least 50 members of the ANC to vote with them to oust the president.

The parliament has 400 members.

Our correspondent reported that the secret vote could "embolden" some ruling party members to vote for Zuma's ousting.

But she also said that the ruling party is confident that Zuma will remain in power until the end of his term in office.