The people charged with protecting New South Wales' national parks have accused the State Government of crippling their ability to contain major bushfires by cutting jobs.

After the NSW Government slashed $40 million from the Office of Environment and Heritage the union responsible for national parks' workers, the Australian Workers Union (AWU), surveyed parks around the state and said that it found more than 130 vacant jobs had not been filled.

AWU state secretary Russ Collison said the union went to every one of their depots and asked them what had happened over the past three or four years.

"They said there's been natural attrition, there's been job vacancies, and they're not being filled," Mr Collison said.

Former field supervisor Nathan Cattell said he left the service in 2012 because jobs were being slashed and the workload was overbearing.

"We wouldn't have the staff to be able to manage," he said.

"Doing your hazard-reduction burning, your law enforcement, your pest control, and your project work to facilitate visitations is just impossible ... it just became very difficult.

"There's guys who have worked in the service for 10-15 years who are looking for other work because they're not coping."

Lives and homes at risk, former worker says

Many national parks border residential areas and former field officer David George said if nothing changed, homes and lives would be at risk.

"It's not a matter of if there's going to be an accident, it's a matter of when, and then the Government will be sitting in front of the coroner," he said.

"There's only so many crews out there and crews wear out very quickly, it is hard, dirty work, there are strict fatigue management out there and there's a reason.

"At the moment with the depleted numbers, as I understand it, you've got less capable people and less people being trained up."

But deputy chief executive of the National Parks and Wildlife Service, Michael Wright, has disputed the union's claims and said there had not been any job cuts.

"National Parks has been relatively stable over the past five years... we haven't reduced staffing levels within the agency," he said.

'Government being tricky with the numbers'

Opposition spokeswoman Penny Sharpe accused the Office of Environment and Heritage of fudging the figures.

"The Government is being very tricky with the numbers, they are including trainees, and they're including temporary positions which are in that mix," she said.

The union has called for an independent audit to settle the paper war, however, Mr Wright said an audit would be a waste of time.

"We're quite certain of the figures we've given the unions already in terms of staff levels and again we're focusing on the awards here, the public would expect the agency to ensure the resources it receives are efficiently and effectively spent," he said.