Disclosures by NSW Government-owned electricity network companies Ausgrid, Endeavour Energy, Essential Energy and TransGrid, released under the Government Information (Public Access) Act, shows just over $4.6 million dollars was spent between 2010 and 2014 on disciplinary and industrial investigations.

An additional $223,832 was spent on private investigators in 2014, with Essential Energy revealing that more than 90 per cent of its spending on these services involved workers being investigated for "alleged non-compliances" with the company's code of conduct.

The GIPA documents, sourced by union representatives, showed Essential Energy paid $1,457,824 for industrial matters, $21,398 for disciplinary, and $67,847 for private investigators.

Ausgrid had spent $1,276,013 on industrial matters, $181,673 on disciplinary matters, and $40,569.20 on private investigators. And Endeavour Energy reported $1,420,000 for industrial matters, $150,000 for disciplinary matters, and $48,149 for private investigators.

Representative from the Electrical Trades Union (ETU) and the United Services Union (USU) said it was outrageous that millions of dollars in public money had been spent by the management teams at the four public companies to investigate their own workforces.

ETU secretary Steve Butler said companies under the control of Networks NSW chief executive Vince Graham invested on average nine times more to investigate workers and unions.

Mr Graham, on leave, was unavailable for comment.

"Networks NSW have been crying poor in recent months, announcing that 2,800 jobs at Ausgrid, Essential Energy and Endeavour Energy need to be slashed," Mr Butler said.

"What they haven't revealed is that they were able to find more than a million dollars a year to spend on external law firms and private investigators."

USU energy manager Scott McNamara said it was particularly concerning to discover that in addition to the large amounts spent investigating workers and their conditions, private investigators had been recruited to "spy" on employees without any disclosure.

"Last year alone, nearly a quarter of a million dollars in public money was handed over to private investigators so they would spy on the hard-working employees of these four companies," Mr McNamara said.

"The fact that such large sums were involved, and the spending was spread across all four companies, shows this approach has become common practice among management teams at war with their own staff."

The Port News asked Essential Energy's deputy chief executive officer, Gary Humphreys if between 2010 and 2014 the company perceived staff behaviour to be a significant problem requiring such an investment of funds and as a result, if that culture had changed.

"The vast majority of our employees come to work each day and carry out their duties in a safe and efficient way on behalf of all our customers," Mr Humphreys said in a statement yesterday.

"Our code of conduct underpins our commitment to fostering a workplace culture that delivers the highest standards of safety, respect, performance and integrity for employees and the customers and communities we serve.

"Unfortunately, claims about the conduct of staff are made from time to time that must be properly investigated."

Mr Humphreys was asked if it was common practice to invest in external law firms and private investigators when addressing disciplinary matters.

"As a state-owned corporation, Essential Energy is obliged to investigate internal or external allegations of breaches of its code of conduct in the interests of transparency and accountability," Mr Humphreys said.

"If an act of wrong doing is reported, an external investigator may be used in some cases to ensure a thorough and independent investigation within the terms of all relevant privacy and disclosure regulations. Like any large organisation, we also have an obligation to carry out pre-employment checks.

"These are legitimate costs of doing business. Our customers and the community have the right to expect that there is probity in a publicly owned organisation."