CAPE TOWN — Over his eight increasingly embattled years in power, President Jacob Zuma of South Africa has fended off five parliamentary no-confidence motions that would have forced him from office. On Tuesday, he is to face another, with a difference: Lawmakers will vote anonymously.

The speaker of Parliament, Baleka Mbete, announced late on Monday afternoon that a vote of no confidence would take place by secret ballot, following a request from a coalition of opposition parties.

More than 60 of the 249 lawmakers from Mr. Zuma’s party, the African National Congress, would have to rebel for the motion to pass — something analysts still deem unlikely. But he may find it harder to contain a bitter factional struggle within the A.N.C., which has dominated South African politics since the end of apartheid in 1994.

Mr. Zuma has come under increasing pressure as evidence of high-level corruption in his administration has mounted, most recently with a trove of leaked emails that appeared to expose the extent of links between senior A.N.C. officials and an influential family, the Guptas.