Management at the South African Post Office (SAPO) on Wednesday said the delivery of mail had been severely affected by strike action.
But officials said they are working towards resolving the issues.
Workers downed tools earlier in February, but SAPO management said it was not clear what the workers were demanding.
The unprotected strike action by employees at several mail services in Johannesburg, Germiston and Pretoria has caused major delays.
SAPO spokesperson Janras Kotsi said services were almost behind by three days.
“We are trying to address the employees to get them back to work.”