The Jobs Action Plan has been subjected to repeated fine-tuning since Premier Mike Baird made it one of his signature policies as treasurer in 2011, with large companies taking advantage of the government's largesse even though it was set up to stimulate small business.

A letter obtained by the NSW Opposition under Government Information (Public Access) laws show that Treasurer Gladys Berejiklian advised the Finance Minister in October last year that there had been a spike in applications after the former chief commissioner removed the time limit on businesses applying to the scheme, which had led to a $130 million "overspend" and would need to be tightened up.

A second document showed that among the 5030 employers that accessed the scheme were three companies with more than 100,000 employees, including a foreign multinational with more than 370,000 staff, before the government restricted it to businesses with fewer than 50 employees in June.

Opposition treasury spokesman Ryan Park said the documents showed the scheme had been distorted into a system of corporate welfare.

"This project was meant to create new jobs," Mr Park said.

"Instead it has created a new million dollar blow out.

"Treasurer Gladys Berejiklian has given the green light for millions of taxpayer dollars going straight into the hands of some of the biggest companies in NSW and Australia."

The Jobs Action Plan originally gave $5000 in rebates on payroll tax to businesses for each staff member that they hired, with employers required to apply within 30 days of the job being created.

Ms Berejiklian increased the rebate amount to $6000 in the June budget at the same time as restricting access to businesses with fewer than 50 employees.

"Businesses across the board are benefiting from NSW's strong economic conditions, but we felt it was important to continue to support smaller to medium firms so that they can keep growing and adding staff," she told Fairfax Media this week.

A de-identified list of companies that accessed the scheme shows that the biggest company in terms of staff to access the scheme had 376,361 employees, and it obtained $13.2 million in tax rebates.

The biggest Australian employer outside the government is Wesfarmers, which has 210,000 employees.

Another company with 15,372 employees obtained $11.7 million through the scheme.

The latest revelations follow data that showed one-third of the companies that accessed the rebates were based in the Sydney CBD and only $24 million out of a total $375 million was paid to small business.

But in the early days of operation the Jobs Action Plan was so under-utilised that the then Chief Commissioner of State Revenue waived the 30-day rule, causing an influx of applicants.

Ms Berejiklian wrote to Finance Minister Dominic Perottet in October 2015 advising that she had approved $130 million to cover the "overspend".

"The former chief commissioner used his discretion to allow employers to lodge applications under the Jobs Action Plan beyond the 30 day rule, irrespective of the length of time that the employment opportunities were created," the letter said.

"This has led to a greater amount of payments this year than expected."

A spokeswoman from the Office of State Revenue said the plan gave an incentive to employers to increase the number of full-time equivalent staff, but the chief commissioner had discretion to accept applications after 30 days.

"Due to an initial low volume of registrations, the Chief Commissioner exercised this discretion – to encourage businesses to register for the scheme and achieve its aim of creating new jobs," she said.

"The scheme performed broadly in line with budget expectations until 2015 when, as a result of careful and close monitoring by the OSR, a spike in registrations was detected."

This prompted the Chief Commissioner to restrict the application period to within 90 days of employment without justification, and this took effect on 23 November, 2015, she said.