Mr Rattenbury has also demanded mandatory pre-commitment in return for his vote, a system by which gamblers must decide up front how much they intend to gamble.

Both were recommendations of a Productivity Commission 2010 report into problem gambling, but neither have been taken up. The $1 a spin limit would allow losses of up to about $120 an hour and would be a big reduction on current bet rates for poker machines, with Canberra's clubs operating machines with a maximum bet of $10 a spin.

Mr Rattenbury holds the balance of power in the ACT parliament and his intervention puts a significant hurdle in the way of the casino's plans to spend $307 million redeveloping the site beside Glebe Park in the city centre, including an expansion of gambling, along with a five-star hotel, six-star luxury villas, seven new restaurants, nightclubs and bars, and a shopping mall.

The casino wanted access to 500 poker machines, breaking the monopoly that clubs have held on poker machines in Canberra. The government knocked back the bid for 500 but has agreed to 200 poker machines, sparkling a fightback from clubs, who are running a campaign targeting Mr Rattenbury and Chief Minister Andrew Barr ahead of the October election. Clubs lobbyist Richard Farmer has also set up a political party, Canberra Community Voters, to field candidates at the election.

The casino submitted its revised business case on June 17, the same day Mr Rattenbury wrote to Mr Barr setting out the conditions for his support. The government is expected to introduce legislation in the first half of August, the final parliamentary sittings before the election, to allow poker machines, and to set special tax rates and a community levy for the casino.

Also this week, casino owners Aquis Entertainment released plans for a new in-house "responsible gambling support centre", including a chaplaincy service. The centre would be on the mezzanine level, close to the gaming floor, and include private counselling rooms, Aquis executive director Jessica Mellor said. The chaplaincy support service would be only the second of its kind in an Australian casino, she said.

Ms Mellor said the plans for Canberra would set a new benchmark and could drive a better approach to problem gambling across the city by the employment of more counsellors, social workers and others with expertise in the field.

Mr Rattenbury's letter to Mr Barr said the Greens were already concerned about the harm caused by gambling in Canberra, with at least 4700 people showing moderate or higher risk behaviour.

As well as mandatory pre-commitment and $1 spins, he wanted other measures, such as limiting jackpots to $500, or a load up limit of $20, or winnings over $250 paid only by cheque (other than for international visitors).

He was also concerned about the casino's request for fully automated table games, and wanted each terminal at an automated table game to count toward the 200 machine limit.

The casino should pay 10 per cent of poker machine revenue into an independently run community fund, and a levy to the problem gambling fund.

A spokesperson for Mr Barr did not answer direct questions about Mr Rattenbury's conditions but said the casino would only be allowed poker machines if it put in place harm minimisation measures and made community donations over and above those made by clubs. It is not clear whether the casino's sponsorship of the Brumbies would count as a community contribution.

Aquis made no comment on Mr Rattenbury's intervention, but said it had proposed tax rates higher than those levied on clubs and had proposed paying a community benefit levy.

Clubs ACT head Gwyn Rees said the risks of problem gambling in a casino environment, particularly on poker machines, were three times higher than in a club.