Correctional Services spokesman Manelisi Wolela has denied allegations that student leader Mcebo Dla.
Members of the South African Municipal Workers Union (Samwu) at Johannesburg Water (JW) have accused the management of nepotism after the appointment of a manager they claimed was a friend of a senior executive.
The row follows the employment in December of Stacy Hoys, who the workers say is a friend of senior manager Jessie Nesamori and is not qualified for the job.
They say the management has failed to act against Nesamori, who recruited Hoys externally and employed her as a manager at JW's revenue contact centre.
They say the minimum requirement for the position is a BCom degree or a relevant national diploma and three to five years experience, which she allegedly does not have.
Qualified internal employees who applied for the position were overlooked and the management admitted that employment policy procedures were not followed in the hiring of Hoys, they say.
JW spokesman Baldwin Matsimela said an internal investigation was under way.
Samwu branch secretary Dumisani Langa said the union was told last Wednesday about the allegations and a dispute resolution mechanism would be sent to JW.