The Local Government Amendment Act scrapped councils' requirement to provide for the "social, economic, cultural and environmental" well-being of their communities.
Instead, councils would have to provide "good-quality local infrastructure, public services and regulatory functions" in a way that was "most cost-effective for households and businesses".
Mr Yule, who is Mayor of Hastings, said this change limited councils' ability to respond to demands from their residents.
"I know councils get into some areas that may not be as core as the past, but they do that because the communities ask them to. And in many cases the Government has failed, the private sector has failed, and people want some things done about it."
In a speech to the conference, Local Government Minister David Carter reassured members, saying that a more focused purpose for councils would not remove local decision-making.
But Auckland deputy mayor Penny Hulse felt the minister had skirted around the issue, and there was still a grey area with regard to what councils' core services would be.
Despite indicating that local government should focus on infrastructure and public services, Government has said councils would still be able to fund fireworks displays under the new reforms, and that events such as the Rugby World Cup and Ellerslie Flower Show would not be banned.
However, councils would be prevented from some investments such as buying foreign farms.
Government believed councils' responsibilities had become too broad and this had contributed to a blowout in rates and debt.
Prime Minister John Key told the conference yesterday [MON] that central government had tightened its belt in difficult economic times and local government needed to do the same.
Mr Yule argued that while the "four well-beings" were responsible for a small proportion of rates rises, the greatest pressure on council spending came from infrastructure demands such as roading.
Local Government New Zealand had also received legal advice that the change would expose councils to legal action.
Ms Hulse said that if councils had to choose the "most cost-effective" option for building a footpath, it could face legal challenges if it failed to choose the cheapest construction option.