Listening devices placed in offices at Causeway Coast and Glens Borough Council made secret recordings of senior officials making disparaging comments about ratepayers and a trade union representative, the Irish News has learned.
The audio clips, which include personal criticism and profanities, single out a well-known community activist and a female trade union representative.
It has also emerged that a senior Nipsa official has written to the DUP mayor of the borough, Ivor Wallace, to lodge a formal complaint.
In the letter, which has been seen by the Irish News, the senior union official said she was writing with "grave concern" about a named colleague.
The existence of the recordings, which is being investigated by the PSNI, was revealed by the Irish News last week.
Sources say they were made over a nine-month period in 2022 after bugs were planted in more than one council official's office.
Sources said that hundreds of hours of recordings were made.
It is understood the devices were later removed by those responsible for placing them.
Sources last night said it is believed one of the bugs was hidden behind a 2020 calendar located in one office.
It is claimed the location was chosen because the calendar hadn't been moved for around two years.
It is also suggested that the device was later removed while the office was redecorated before being returned to its original hiding place.
Details of the recordings were posted online last week.
Around the same time the recordings were put up an email entitled ‘Whistleblower 2’ was circulated to elected representatives and staff members.
The message includes a summary of the conversations alleged to have taken place and partial transcripts of the exchanges.
During one conversation stinging and cruel comments are made about a female trade union representative.
A local community campaigner and businessman is also described using four letter words and other expletives while the entire population of Portrush is singled out for criticism.
In the letter to Mr Wallace, a Nipsa official said the union was aware of "appalling conversations" between three named members of council staff.
The letter said the conversations included the use of "extremely derogatory and profane language" about the official which has had an "extremely negative impact".
It also claims that "derogatory and offensive comments were made about other female Nipsa members employed by the council."
Mr Wallace last night confirmed he had received the letter.
"I have passed that on to our human resources...to see what way we are going to go with it," he said.
"It's obviously an official complaint."
The council was contacted for comment.
