One of South Africa's largest public sector unions on Monday gave notice of its intention to strike after rejecting a 3% wage offer from the government.
The Public Servants Association (PSA) says the walkout could take place November 2, potentially affecting service delivery across government departments.
Salary negotiations began in May, with unions initially demanding a 10% increase, but this was later revised down to 6.5%.
The government's offer to public servants included a once-off cash payment of 1,000 rand ($55), but unions say that does not materially improve their income.
"As long as the cash gratuity ends next year March they (PSA members) won't accept the deal," senior PSA official Reuben Maleka told Reuters.
Most unions in the country's largest labor federation COSATU, which is in an alliance with the governing African National Congress, have also rejected the government's wage offer. But they are yet to file a notice that they intend to strike.
The government had hoped to conclude wage negotiations ahead of its mid-term budget on Wednesday, but with the deadlock in wage talks that is unlikely to happen.
The government has been trying to keep a lid on rising civil servants' salaries as part of efforts to contain recurring budget deficits.
The public sector wage bill makes up about one-third of total government expenditure.