Gaming Technologies Association chief executive Ross Ferrar said the ACT's pursuit of a separate set of rules for the casino had been "a source of great frustration", and unless $5 spins were abandoned, or the same restrictions were introduced citywide, poker machines would not be viable.

"It is very difficult for us to understand how it would be possible to provide the Canberra casino with unique games with unique machines at a cost that would be anywhere near capable of sustaining a business case for their purchase," he said.

"Developing a game for a poker machine is a complex and very expensive process."

Mr Ferrar's comments put a question mark over a project that has already made only slow progress since the casino announced plans in 2015 for a major expansion with swank hotels and brand shopping, dependent on being given the right to operate poker machines. Clubs are fighting hard to maintain their monopoly and the Greens say they will only support the move if the casino's have a spin limit of less than $5, compared with the $10 spins in clubs, and the first mandatory precommitment scheme in the country, with gamblers forced to nominate upfront how much they are prepared to lose on the pokies over 24 hours.

The government introduced a bill in August, but it leaves the difficult questions unresolved, such as the spin limits, tax rates and how much of the redevelopment will go ahead. The bill includes $5 spins by the government and the Greens are still negotiating.

The Gaming Technologies Association, which represents the big poker machine manufacturers including Aristocrat, has rejected the regime.

"The bill would result in the equivalent of a miniature, separate casino jurisdiction with unique requirements. The process of developing a unique portfolio of games for such a jurisdiction is not financially feasible," Mr Ferrar has told the ACT government's justice directorate in answers last week to a series of questions.

Mr Ferrar told The Canberra Times that some jurisdictions had $5 spins, but the games had to be separately developed and tested, then externally retested for each jurisdiction based on the rules of each, adding layers of complexity and expense. If the ACT mandated $5 spins, games would need to be developed and rested all over again - which would not be feasible for a single venue with just 200 machines.

The games from Victoria and Queensland could not be easily transferred to the ACT, he said, comparing the different rules to different railway gauges across the country.

"You would have 200 machines with their own unique set of requirements. How can you build a business case to spend hundreds of thousands of dollar developing a unique set of games for Canberra casino?"

There was no technical barrier to providing the games, but there was a clear cost barrier and suppliers would have "great difficulty" offering games to the casino at a reasonable cost.

It would be different if the lesser spins applied across the territory's 5000 machines, including in clubs. Specific games had already been developed for Canberra's clubs, and with that number of machines the work to develop games was viable.

But the existing $10 spins were the best option, keeping everyone happy - the clubs, the casino and the players, he said.

Mr Ferrar also rejected mandatory precommitment as "contrary to the concept of hospitality". It could make things worse for problem gamblers who would often set very high limits, or fraudulently obtain multiple account cards and interpret the system as a challenge to spend more money and time.

Mandatory precommitment would require a centralised monitoring system and the replacement of all games and machines.

"Australia's poker machines are the slowest gaming machines in the world and their maximum bet limits are among the world's lowest," he said. "... Reducing the maximum bet beyond current levels will remove poker machines from recreational players' entertainment options and could exacerbate negative consequences for problem gamblers."

ACT Greens gambling spokesman Shane Rattenbury dismissed Mr Ferrar's concerns as "the kind of self-serving response you'd expect from an association whose business model is designed to extract money from problem gamblers".

A spokesperson for Attorney-General Gordon Ramsay said the ACT and NSW were the only jurisdictions with a $10 limit per spin; everywhere else had a $5 limit, and as a result most games were developed with a bet of $5 to $10.

A central monitoring system allowed bet limits to be changed and would be needed at the casino, he said.