A grieving family is calling on a local council to be investigated after a staffer took his life following a decade of alleged workplace harassment and bullying.

David Wilson, 61, worked at Wollondilly Shire Council in Sydney's south-western fringe as a plant operator for 15 years.

He took his own life in June 2018 on the same day he was told that his most recent complaint about harassment within the council was unsubstantiated.

The complaint was investigated by an external group.

"I got a text that morning and the text said, 'today I got the straw that broke my back', and he said goodbye," his wife Debbie Wilson said.

According to documents obtained by the ABC, Mr Wilson claimed he was taken aside and given "a veiled threat to [his] employment" after he raised issues around "morale and a loss of work conditions" at a staff meeting.

In the handwritten complaint, Mr Wilson claimed he felt "intimidated" by the exchange and was "gobsmacked" given "all our training on code of conduct, workplace bullying etc".

Ms Wilson said her husband of 42 years made numerous verbal and written complaints since 2008, when the alleged bullying began.

Handwritten diaries
In diaries dating back to 2008, Mr Wilson documented his "loss of sleep" and "feeling sick with worry" over the bullying he experienced at work.

In hundreds of entries, he described being hounded about his punctuality, his personal life and at times, being physically harassed.

In one entry in 2014, he described a colleague squeezing his right shoulder "still tender" from recent surgery.

In several separate entries, Mr Wilson wrote of homosexual slurs made against him within the workplace.

He described one incident where he was allegedly asked "isn't it time you came out of the closet?" and "who did you turn gay for?"

Mr Wilson also detailed his distress at disturbing graffiti on the walls of local toilet blocks.

"He'd go into the toilet there and there would be his work phone number on the wall, [and] 'if you want a good time call David'," his mother Margaret Summers said.

"Then he changed his number but see the problem is at his work, because he's a truck driver, they had to put his name and phone number up on the board."

Despite having his number changed several times since the graffiti first appeared in 2008, Ms Wilson said her husband often received late night phone calls and offers of a "threesome", and found it unbearable.

"It was a work-issued phone, so it was obvious someone was taking his phone number from the notice board and was putting it on the toilet walls within the local Wollondilly shire," Ms Wilson said.

"He was issued with another phone and it went back up on the walls again, but it hurt him even more, because they wanted a threesome, which involved me into it as well.

"He was totally devastated about it," she said.

Ms Wilson said the couple separated in October 2017 after Mr Wilson slipped into a deep depression.

He turned to alcohol, which Ms Wilson believed was triggered by prolonged workplace bullying.

"Each time problems [at work] came up his depression got worse," Ms Wilson said.

"We just felt that we needed to have a break so David could get his drinking under control and he did."

Ms Wilson said her husband felt defeated that his complaints about a toxic culture within the organisation fell on deaf ears.

"They gave him no duty of care, there was no support," she said.

"They knew he was depressed and they weren't there for him."

Wollondilly Council declined to comment on David Wilson's case in respect of his privacy but Mayor Judith Hannan said any complaint around bullying or harassment at council was taken seriously.

"We have no tolerance to bullying at all and we encourage all of our staff, if they have an issue, to certainly speak up," she said.

The council is currently undergoing an external workplace review.

"We have an investigation underway, external to council, and we're looking at all of our policy and procedures about reporting so that we have best practice in this area," Cr Hannan said.

She said Mr Wilson's death had a great impact on staff at the council, and members of the local community.

"His workmates really respected him and they feel his loss, like the rest of us," she said.

But Ms Summers is calling for the council to be investigated as she believes it had a culture of bullying which became a catalyst for her son's death.

"I do truly believe they need to be investigated and find out actually what has been happening," Ms Summers said.

"There's nothing we can do for David, but we might save somebody else."

The ABC understands officers from New South Wales Police have possession of several documents, including many of Mr Wilson's diaries, and have spoken to his immediate family.

A report is being prepared for the state's Coroner however it could take several months to decide if an inquest into the death should be held.

Mr Wilson's sister, Margaret Shumack, said she would like the council to be put under a microscope so that her brother's death would not be in vain.

"There was nothing done. No one was listening," Ms Shumack said.

"They need to stop it from happening to someone else. They need to be accountable for it."

Bullying compensation claims high in local government
According to the latest data from Safe Work Australia, local government employees are the third most represented group when it comes to compensation claims for workplace bullying and harassment, behind emergency services and aged care workers.

For the three years to 2016, about 190 local government employees received compensation for bullying and harassment at work each year.

For every 100 million hours worked there were more than 40 claims from within local government organisations.

Aged Care and Emergency Services workers had the highest number of claims with more than 300 accepted per year or almost 50 claims for every 100 million hours worked.

United Services Union (USU) organiser Rudi Oppitz said he was not surprised by the data.

"I've been an official for over 25 years and certainly in the last 10 years, the vast majority of the matters I deal with are matters relating to allegations of harassment and bullying," he said.

"There needs to be a better way of dealing with these matters.

"There needs to be better training. There needs to be better enforcement at the management level against those employees who are complicit."

'Previous claims of harassment and bullying'
The USU assisted Mr Wilson with his final complaint to the council and Mr Oppitz said he was left with several questions about how the allegations were handled.

"The number of people who were interviewed was probably not the full scope of people who could have been interviewed," he said.

"So there were some concerns around how that interview was conducted and whether or not it was a full and proper investigation."

Mr Oppitz said he was aware of several staff at the council who had reported bullying and harassment.

"There are have been previous claims of harassment and bullying over a period of time," Mr Oppitz said.

"From what I've been told from my members, there have been complaints made."

Former Wollondilly councillor Ray Law agreed with the union.

Mr Law successfully ran for council on an anti-bullying ticket in 2012.

"There was a culture that I believe was one of bullying and quite serious harassment," Mr Law said.

"So part of my platform and standing was to bring that into the open and see what we could do about changing it."

Mr Law said he resigned from his post in July 2017, frustrated by his inability to address the alleged culture of bullying within the council.

"I know my own period on council was one filled with frustration and regret," Mr Law said.

"I did warn the council there would be consequences but never in my darkest nightmare did I ever feel it would get to this point.

"There needs to be a complete culture change and it needs to change from the very top."