Unions New South Wales says it is concerned about the safety of workers at four power plants that have been the subject of an extortion attempt.
Delta Electricity says the threat was made to sabotage its power plants and substations unless payment of an undisclosed amount of money was made to the extortionist.
Security has been increased around the company's power stations in Lithgow in central western New South Wales and Lake Macquarie on the central coast.
Delta Electricity produces around 12 per cent of the electricity needed for the country's electricity market.
The secretary of Unions New South Wales, John Robertson, says the incident has been unnerving for staff working for the company.
"It's always an uncomfortable situation but by the same token the staff are not going to be intimidated by these sorts of threats," Mr Robertson said.
"It is one of those things that we're always concerned about where staff's safety is put at risk or their safety is threatened. Frankly acts like this put everybody in a very difficult situation."
Mr Robertson says he is confident that Delta Electricity has responded appropriately.
"We are concerned obviously when any threat like this is made, particularly where those threats could have a direct effect on workers and their safety."
Lithgow Mayor Neville Castle says residents are worried about the threat.
"Obviously there's concern in the community," Mr Castle said.
"We'd look at it very dimly however to my mind it wouldn't be concerned with terrorism activity because as far as I am aware, terrorists don't forecast what they are goring to do in advance. It seems to be very sudden as to what they do."
