Poker machines at Crown Casino were deliberately manipulated and tampered with by technicians in a bid to boost profits, another whistleblower says.

The whistleblower who worked at Crown in Melbourne for many years added weight to testimony made by three men against the casino that was tabled in Federal Parliament by independent Andrew Wilkie in October.

The claims by those three former employees — that machines were manipulated, federal anti-money laundering rules were avoided, and a blind eye turned to domestic violence and illicit drug use — triggered an investigation from Victoria's Commission for Gambling and Liquor Regulation (VCGLR).

Crown Casino emphatically rejected all the allegations and took out newspaper ads rejecting the claims.

In ads published in October, Crown Resorts executive chairman John Alexander said that if Mr Wilkie "believes he has evidence of wrongdoing, he should stop the political games, step out of the Parliament and make his claims without privilege".

But in a one-line statement in response to the fourth whistleblower's claims, a Crown spokesperson said "any allegations of this nature should be to be referred to the VCGLR".

In an interview with the ABC, the new whistleblower said last year he and other technicians were instructed to remove betting options on the Players Choice Super machine because punters were winning too much.

"There was an instance where this particular game was paying out too much on the gamble function so technicians were instructed to remove the gamble button completely," he said.

"It was physically removed."

In another case he said technicians removed multiple "spin" options on the IGT Blue Chip machines so that only the maximum bet and minimum bet options were left.

The claims are consistent with the October trio's testimony that many gambling options were removed.

The original three whistleblowers accused the VCGLR of not following up issues of button manipulation when it was detected.

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He said the technicians were instructed to make the changes.

"The reason behind that was to limit the play options for the players, to encourage them to play maximum lines and of course win maximum amounts of money," he said.

The fourth whistleblower has not spoken to police because he is worried about being identified to powerful people at Crown Casino, and has fears for his safety.

"I knew that it was unethical when I heard about the conversation with the analyst saying it was to encourage players to spend more money and limit their play options," he said.

"Obviously from anyone's perspective who hears that, it is not the right thing to be done."

He believes there should be a paper trail of evidence about the manipulation and said the order came from managers.

The whistleblower also confirmed the practice of moving poker machines into the highest traffic areas of the Casino on weekends and resetting the "return to player" ratio to maximise profits.

Under Victorian law, pokies must return a minimum of 85 per cent of money wagered to punters.

Most machines operate at a higher rate, but under a strategy used by Crown, the whistleblower claims, machines were regularly reset to the 85 per cent ratio on weekends to boost revenue.

"Not only moving machines into highly populated areas but there were instances where machines were wiped of their memory and the percentages returned to player percentages modified over a weekend period and lowered," he said.

There had been attempts for the fourth whistleblower's claims to be tabled in Parliament but this was blocked — Mr Wilkie's office has since handed that evidence to Victoria Police.

Independent MP Andrew Wilkie tried to table the fourth witness's testimony in Parliament. ( ABC News: Nick Haggarty )

Mr Wilkie said the latest allegations were very serious, but acknowledged he did not know if they were "true or false."

"The next layer that's required is a [federal] parliamentary inquiry because that will provide a framework for these and other whistleblowers perhaps to come forward and, with the protection of Parliament, to tell us what they know," he told ABC News Breakfast.

Earlier this year, more than a dozen technicians were laid off by Crown but an Electrical Trades Union campaign against the Casino has resulted in the company offering the staff their jobs back.

The retrenched staff are being offered $10,000 as compensation or $20,000 if they do not return. The offer was only made after the three whistleblowers made their claims.

The whistleblower is angry that Crown has been so dismissive of the claims.

"It's very frustrating and disappointing that someone can so blatantly come out and say that it is a lie when I know it's the truth," he said.

Greens call for police investigation

The VCGLR said it was not appropriate to comment due to their ongoing investigation into the matter.

"An investigation is currently underway on matters relating to the claims made by Mr Wilkie in Federal Parliament," a spokesperson for the commission said.

Victoria's Gaming Minister Marlene Kairouz said she had confidence in the regulator to investigate the claims.

"The regulator is taking these allegations quite seriously, so am I," she said.

"They're investigating these allegations quite thoroughly. I've asked them to leave no stone unturned."

But Greens MP Colleen Hartland said Crown's poker machines should be suspended from trade and the police brought in to investigate.

"The minister shouldn't be just relying on the regulator, which clearly isn't doing its job," she said.