Union officials said an eighth round of talks on wage demands ended without agreement and that they would now decide what action to take.
"A strike is very likely, indeed it is on the cards if the government doesn't change its position at all," Fikile Majola, general secretary for the National Education Health and Allied Workers Union (Nehawu), told Reuters.
Unions said the government had failed to put any new offer on the table. Workers are demanding a 9% to 7.5% sliding-scale wage increase and a three-year framework agreement that allows for negotiations on actual wage increases.
The government has offered workers a 5.5% general salary raise and three-year wage agreement linked to inflation, which is currently running at 6.3 to 6.4%.
"The government came back today and put exactly the same position back on the table," Majola said.
"They also put a new matter on the table, which is to do with restructuring and service delivery, and we have said that we want to discuss this. But it still doesn't address our wage demands."
Nehawu, which accounts for 240 000 of the 1.1 million public service workers that the unions represent, earlier said it would only consider modifying its own demands if the government also moved significantly from its present position.
Majola said five of the 12 public sector unions involved in the bargaining would meet on Thursday to discuss what position they would take to members and other unions. A decision on what action to take would be made early next week, he said.
Strike season
The strike, which would include teachers and health workers, could be highly damaging if it repeats those of previous years. Union officials said on Tuesday that the sluggish progress in talks already seemed to be following the pattern of those of the past two years.
South Africa lost 3.1 million worker-days due to strikes in 1999, the worst level since apartheid ended in 1994. Public servants took to the streets demanding higher pay.
Gold and coal firms narrowly avoided strikes last month, while a week-long dispute at South Africa's number two steel producer, Highveld Steel and Vanadium Corp Ltd, ended on Tuesday after unions agreed to higher wage offers.
A nine-day auto industry strike, which manufacturers say has cost them over R1 billion ($121 million) in lost turnover, was close to resolution on Wednesday after labour officials signalled they were ready to revise their demands.
Around 3 000 workers remain on strike at Hulett Aluminium and another 5 400 have downed tools at Northam Platinum in disputes over wages.
The public sector talks come ahead of the start on Thursday of a protest action by 1.8 million-strong labour federation the Congress of South African Trade Unions in the run-up to a strike on August 29-30 in protest at privatisation.
Cosatu's action will be the first such co-ordinated move against the government's efforts to restructure and partially privatise more than R170 billion worth of assets inherited from the previous government.