The rise of psychometric screening of job applicants, budget cuts, and the end of entry-level clerical jobs have been blamed for the increasing disappearance of employees with a disability from the NSW public service – Australia's largest employer.

The latest data shows the percentage of Public Service Commission employees with a disability has halved in two years, falling from 8.6 per cent to 3.8 per cent in 2014.

Across all NSW government departments, disabled employees have fallen from 4.8 per cent of the workforce in 2009 to 2.9 per cent this year.

"It is shocking that the Public Service Commission is one of the worst offenders, even though it is responsible for helping other government agencies address barriers to employment for people with disability," said NSW Labor's disability spokeswoman, Sophie Cotsis.

People with Disability Australia president, Craig Wallace, said: "Governments should not be calling for people to get off welfare, and for private employers to step up, if they are not employing people with a disability themselves. This has become so bad and the numbers are so low that we need to be looking at quotas or targets."

Mr Wallace quit a 15-year career in the Australian Public Service in 2010, after he was moved to a building without a disabled toilet.

Lack of support is driving disabled workers out of the public service, he said.

"If you can't get a carer to get you out of bed in the morning its hard to maintain a reliable job where you need to be there at a particular time. Its also partly about the way the workforce has changed," he says.

"The basic level positions that people with a disability came into the public service with have disappeared. There is also an increasing tendency for public sector employers to use assessment centres or pyschometric testing that tends to screen out people with a disability.

"It is a management problem – they used to recruit for a position, now they recruit for a range of criteria, you have to be good at working in teams, for example, or problem solving, when in fact what they just need is someone to do a specific task that someone on the spectrum could do."

PricewaterhouseCoopers director Cain Beckett, who was born with cerebral palsy, says: "When it comes to disability employment, we are about 60 years behind gender diversity. One in two disabled people have a job."

Mr Beckett sits on the NSW government's Disability Employment Advisory Committee.

"The government is recognising that unless there is a focus on it, an active strategy, the numbers will slip backwards because of people's in-built bias," he said.

The former disability discrimination commissioner, Sev Ozdowski, says governments have done little to address the problem, and "awareness raising does not translate into real employment".

"They are the biggest employers in Australia," he said. "They should do more."

The director of equity and diversity at the University of Western Sydney, Dr Ozdowski, says the reason for the drop could be the perceived risk for managers employing a disabled person amid cost-cutting.

He said it was unjustified, and based on ignorance, but could be overcome by creating a pool of money under the department secretary's control for hiring people with a disability.

Disability Minister John Ajaka said: "These statistics show that as a government we can do better, and I am determined to improve employment prospects for people with disability in NSW."

Mr Ajaka​ said the Disability Inclusion Act now requires departments to complete an action plan. The plans are due in December.

Under the former Labor government, the public service had a goal to employ 4 per cent of employees with a disability.

Quotas for disabled public servants are used in nations including Thailand, Taiwan, Japan, India, Spain, Bangladesh and Nepal.

A Public Service Commission spokeswoman said the NSW public service "has experienced declining rates in the reported numbers of employees with disability since 2006, despite targets and benchmarks that have been in place".