On Friday the Andrews government announced the fund was "fully subscribed" and will close on July 18. Almost 16,000 payments were made to employers hiring disadvantaged job seekers since it started in April last year.

State Revenue Office figures show about $40 million has been handed over, with the number of payouts rising sharply from early this year after the government flung open the eligibility criteria after a slow start.

On Monday Shadow Treasurer Michael O'Brien said he would write to the Victorian Auditor-General asking for a full investigation, claiming the Opposition had been handed evidence suggesting "serious rorting has occurred".

Mr O'Brien declined to provide details of the allegations, but said the evidence suggested "agents" had been paid by the government to promote the scheme "to try to get money out the door as quickly as possible".

"We are aware of businesses that have employed people [who] at the time ... were not eligible to receive back to work payments," he said. "Months after those people were employed they were contacted by a third party advising that they should apply for a back to work payment. This payment was approved."

Mr O'Brien also raised questions about why only $40 million out of the $100 million fund had been allocated.

A government statement released on Friday said the fund set aside $15 million for dairy and automotive workers, $15 million to support disadvantaged workers through Jobs Victoria and $6 million for pilot intervention programs in disadvantaged areas.

It is understood the remaining money in the fund will be used to cover second instalment payments to employers who can demonstrate that they have kept workers on for at least nine months.

A spokesman for Mr Pallas said the government made no apology for training and improving the skills of unemployed and disadvantaged workers.

"Unlike the Liberals who slashed funding for training and TAFE,  we're focused on giving Victorians the best chance to get back to work," he said.

Announced in the lead-up to the 2014 state election, the scheme underpinned a Labor promise to create 100,000 full-time positions within two years. Since the election, the state's unemployment rate has fallen from 6.6 per cent to 5.8 per cent, with the number of full time jobs up 72,800 since December 2014.

After a slow take-up rate, the government beefed up the scheme earlier this year, significantly lifting payments for business hiring and training young unemployed and retrenched workers and the long-term unemployed.

Eligibility for the scheme was also expanded to not only include the long-term unemployed, young people and recently retrenched people, but also refugees, sole parents, pensioners, disability pensioners, Aboriginal unemployed and drought-affected households.