The South African Municipal Workers' Union is demanding the suspension of Durban metro police chief Vincent Ngubane, who has been accused of sexual harassment by a junior police constable.
The incident allegedly took place in March.
Union representatives, metro council CEO Eddie Morton and the city's legal unit interviewed the constable on Friday, after she lodged a formal grievance in which she claimed Ngubane forcibly had sex with her, before promising her a more lucrative post in exchange for her silence.
The council's executive committee is expected to take a decision on the allegations this week, before an internal inquiry is launched.
In an affidavit forwarded to Morton, the constable, whose identity is known to The Mercury, claims the incident happened on March 10 when Ngubane went to her flat.
Afterwards, the constable threatened to report the incident. But Ngubane apparently begged her to keep quiet, promising her a permanent post.
Contacted by The Mercury on Sunday, Ngubane said he had not been formally charged and was unable to comment.
Attempts to reach Wiseman Mchunu, the union's shop steward representing the constable, were unsuccessful. But Richard Hlophe, the union's provincial secretary, said: "If the allegations are true, we will not rest until the law has taken its course."
On Monday, the union was to challenge the council to suspend Ngubane.
Hlophe added that he was not party to concerns expressed by some union members, who were reportedly unhappy about the matter being dealt with in public.
They believed it would tarnish Ngubane's reputation. Ngubane was previously supported by the predominantly black union.
Hlope said: "In terms of a metro council policy on sexual harassment, accusations relating to sexual harassment are viewed in a serious light, more especially if senior employees appear to demand sexual favours in exchange for promoting victims.
"This is a junior constable working part-time and wanting a full-time contract. She was vulnerable to such alleged victimisation."
Ngubane rose up the corporate ladder in 1998 when he was given the task of overseeing policing at the beachfront.
Before long, he became deputy chief constable. He became the chief constable in May, when former chief constable Alf Taylor retired.