The Public Servants Association says its fresh round of public protest and strike action is in part aimed at taking on what it calls Cosatu's "toxic majority" among public servants.
Earlier on Wednesday, the union announced it would begin its strike action on Monday 11 June, starting with protests on what it termed a "Day of Rage".
Cosatu, in response, said the PSA should stop trying to drag the federation into their strike.
Some 5 000 of its members working at the South African Social Security Agency (SASSA) had also given notice to strike, it said.
The strike is timed to coincide with a 21-day period during which other unions in the public sector are set to consult with their members.
Speaking to Fin24 ahead of a media briefing on the intended strikes, the union's deputy general secretary Tahir Maepa said the PSA wants to reduce Cosatu's "toxic majority status" among public servants.
"They may be big now, but they may not be big tomorrow," Maepa said.
Alliances should not be allowed to "take precedence over the prosperity of public servants", he added.
Fin24 previously reported that although the PSA doesn’t constitute the majority of civil servants, it has warned that the union has members in key sectors such as immigration and the courts, and will shut these services down through industrial action.
The PSA is the largest of the non-Cosatu affiliated unions.
It has consistently accused Cosatu-affiliated unions of being on the side of government.
Maepa vowed to chip away at Cosatu's majority. The PSA was proud of the pressure it had applied thus far, he said.
And the pressure was "working", he said.
"There is a misconception by the Minister [of Public Services and Administration Ayanda Dlodlo] and Cosatu that this strike may be illegal or not in the interest of the public servants, or that the PSA has abandoned the rules that were agreed upon," said Maepa.
"It is clear they [Cosatu] are trying to save the state money."
Maepa predicted that if wage negotiations were not solved now, additional problems would arise down the line.
Implementing the three-year wage deal unilaterally in the first year would not solve the issue because the second and third year were intended to be implemented by agreement, he argued. "Come the second and third year, we will be in the same position," he said.
'Leave Cosatu out of it'
In response to Maepa's claims, Cosatu spokesperson Sizwe Pamla said PSA was "welcome to go on strike and represent its members".
"What is problematic is that they want to prescribe to Cosatu members and unions what to do," Pamla said.
"They have a federation called Fedusa and they should be focusing on their federation.
"Cosatu does not [have] an affiliate called PSA and we do not understand why they want to drag our federation into their strike.
"Cosatu unions will communicate their position when the 21-day consultation period has expired."
Continuing to strike could have a financial impact on public servants, Cosatu argued.
"Cosatu unions demanded CPI (Consumer Price Index) plus 2% increase and government offered salary level 1-7 […] CPI plus 1.5%.
"We have many highly indebted public servants, and we cannot lead them on a strike for 0.5%, while the strike principle of a no work, no [pay] will be applied," Pamla said.
"Strikes are not about street therapy, but are about improving the earnings and working conditions for public servants.
"Let PSA go on strike and achieve the mandate from its members and leave Cosatu out of it."
The deal signed by certain unions will see 7% increases for junior employees for 2018/2019, backdated to April 1. Mid-level employees will receive 6.5% increases and senior staff will have raises of 6%. The increases for the second and third years of the wage agreement are on a sliding scale.
The PSA, however, is holding out for a 12% increase across the board for its members.
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