Prime Minister John Key says the Green Party's proposed measures to combat problem gambling are not realistic.
The Greens are proposing mandatory measures to limit what gamblers can spend on electronic gaming machines from 2017.
They propose the introduction of pre-commitment cards that require people to enter their spending and time limits.
Mr Key says it might be a nice idea, but people would find other ways to bet where there are no such limits, like online gambling.
"There are no restrictions on that, I can't even fathom to work out how you would restrict online gambling, and so it's a bit farcical to say that you could only go to the casino and spend this amount of money but, by the way, in your home you could bet away your entire net worth."
Problem Gambling Foundation chief executive Graeme Ramsay insists the spending and time limits would make a difference by preventing problems with betting.
"A problem gambler will find a way around any system, but the real impact of mandatory pre-commitment system is actually to stop people developing problems in the first place. They're actually a precautionary measure rather than a treatment measure."
An associate professor in population health, Peter Adams, says the pre-commitment cards and player tracking are the most promising harm-minimisation measures around for problem gambling, and he fully supports the proposals.