"It's going to have quite a major impact for all managers and potentially councillors," said Mr Buchanan.
"You become personally liable which I don't like."
At present the council requires contractors to show they have a health and safety policy as part of their bid for the contract.
"That's as far as it goes," he said. "You are not actually responsible for them.
"Under the new process, there's a much more direct connection."
At a council meeting on Wednesday, Mayor Adrienne Staples said she was concerned about the cost of administering a chain of responsibility.
"It could end up costing us in terms of making sure it happens," she said.
Councillor Max Stevens said council would need to have a detailed system to track decision-making - a paper trail essentially - and show it was being responsible.
Mr Buchanan said the Government was right to reform the laws.
"It is born out of a serious event, you can say it is pretty tough but there are 29 people dead because of the weaknesses in the law."
He said he had just been working through a new health and safety policy and had to put it on hold.
He was not yet sure exactly how much it would cost council to undertake the new reforms and what would need to be done.
"We will know exactly what's required when the final bill is ready."
The law changes could trickle down to small organisations associated with the council, said Mark Allingham, group manager infrastructure services.
For example, he said, if a group like the Lions cut down a tree for council and something went wrong, council could be responsible. "It's going to be a major issue."
The Government had its third reading of the WorkSafe New Zealand Bill, Health and Safety in Employment Amendment Bill and Mines Rescue Bill in November last year.
These will replace the Health and Safety in Employment Act, which is over 20 years old.
The changes are expected to be passed into legislation this year.