Listening devices were reportedly placed in offices at Causeway Coast and Glens Borough Council, it's understood.
According to the Irish News, the devices made secret recordings of senior officials making comments about a female trade union representative and ratepayers.
Certain clips are alleged to include "derogatory and profane language".
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The Irish News revealed the existence of the recordings last week.
The paper reports that sources say hundreds of hours of recordings were reportedly made over a nine-month period in 2022. It's said the listening devices were planted in more than one council official's office and were later removed by those who placed them there.
Details of the recordings are reported to have been posted online last week, with an email titled ‘Whistleblower 2’ understood to have been circulated to staff and elected reps round the same time, including a summary of conversations alleged to have taken place and partial transcripts, according to the Irish News.
It's reported a local businessman and community campaigner 'is described using four-letter words' and the Portrush population is criticised.
The Irish News also report a senior Nipsa official has written to the Mayor Ivor Wallace to lodge a formal complaint. The letter is understood to have said she was writing with "grave concern" about a named colleague and said Nispa was aware of "appalling conversations" between three named members of council staff.
The letter to the Mayor from the union official is also reported to have said that the conversations included "extremely derogatory and profane language" regarding the official, which has had an "extremely negative impact".
According to the Irish News, the letter also claims that "derogatory and offensive comments were made about other female Nipsa members employed by the council".
The paper added Mr Wallace last night confirmed he had received the letter and reportedly said: "I have passed that on to our human resources...to see what way we are going to go with it.
"It's obviously an official complaint."
The Causeway Coast and Glens Borough Council has been contacted for comment.
A PSNI spokesperson said: "A matter was brought to the attention of police on Monday 23rd January. A number of enquiries were conducted at that time but no further offences were detected.
"New material was submitted to Police over the last number of days and will be reviewed in due course."
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