The union, which represents 44,000 workers, said workers at South African fixed-line group Telkom will strike in four of South Africa's nine provinces on Aug. 3 and Aug. 4 to push their demands for pay increases.
We expect that quite a sizeable number of our members will stay away from work, CWU General Secretary Gallant Roberts said.
The strike action at Telkom, Africa's biggest fixed-line telephone operator, will come only days after a five-day strike by tens of thousands of council workers ended following a wage agreement.
The CWU is demanding that Telkom first move employees from lower to higher pay scales before implementing a 7.5 percent wage increase.
The wave of strikes in South Africa last month challenged Zuma's economic policies as the unions that helped bring him to power in April elections flexed their muscles, seeking payback for their support.
The council strike left rubbish piled up on streets and licensing offices closed. Workers settled for a 13 percent pay rise, almost double the inflation rate.
Double-digit pay settlements in the private and public sectors could put added strain on the economy, which is in its first recession since 1992 because of reduced local and global demand.
Analysts said above-inflation increases such as the one won by the council workers could compound the impact of a 31.3 percent increase in electricity prices granted to power utility Eskom last month and push inflation higher.
Pressure on the government has also come from poor township residents, who have demonstrated to back their demands for better living conditions for millions of blacks who still lack adequate housing, electricity and water 15 years after the end of apartheid.
(Reporting by Marius Bosch; Editing by Ron Askew)