The National Union of Public Service and Allied Workers (Nupsaw) on Thursday rejected the public sector pay agreement.
The three-year agreement has been hailed by Public Service and Administration Minister Lindiwe Sisulu as allowing government to change the way it works.
Nupsaw, which has a membership of 30 000 said it was unhappy about a pay progression plan for workers who get promoted.
“We are informing the public servants that they are being taken for a ride, they are not being told the full truth and an interpretation is being put to them,” said the union's General Secretary Success Mataitsane.
Congress of South African Trade Unions’ Patrick Craven said this agreement could be a turning point.
“We hope that this will mean that we can now focus on importing the quality and we hope that the private sector will take note of the increase.”