Te Tuinga Whanau Support Services Trust executive director Tommy Wilson told the Bay of Plenty Times Weekend the new law would be "as effective as a packet of wine gums to cure a hangover" in tackling under-age drinking.
"Green-lighting grog by imposing a stupid law like the 'ask your mummy first' one [solves nothing]," Mr Wilson said.
"It is beyond belief. It smacks of the smacking law. The only one to benefit from this law is the booze barons who sell it.
"Until we can treat all drugs as drugs - be they medicinal, recreational, illegal or legal highs - we will keep pushing the problem from one policy-maker to the next."
Get Smart Tauranga Drug and Alcohol Services manager Stuart Caldwell said parents would need to ramp up their communication with their teenagers.
"With a real and serious threat of prosecution, parents will think twice about where their children are."
Parents would have to be "very specific" in their permission for their underage children to drink alcohol.
"Parents who have another parent's underage young people over at their home drinking will also have to be seriously vigilant around whether or not they have permission to supply them with alcohol, as they risk prosecution without this.
"It is parents or legal guardians who can give permission. This means 'court appointed legal guardian', not the babysitter."
The law was a positive move in the right direction, Mr Caldwell said.
But it would remain to be seen if fines were imposed and the law was policed.
"It will take time to establish [a precedent], but in my view it does have the teeth to produce effective changes."
Mr Caldwell said 75 per cent of alcohol consumed by underage drinkers was given to them by their parents.
Jackie Paine, who runs parenting courses for The Parenting Place in the Bay of Plenty, told the Bay of Plenty Times Weekend the law put responsibility back on to parents.
It had the potential to help parents by providing a "back-up" to their own rules, she said.
"It could have a lot of parents saying that's great, because you have got back-up to say to the kids 'no I can't supply you because we have to have your parents' permission'."
But it was possible the status quo could continue, she said.
She advised parents to ring the parents of their children's friends to ask about rules for the party, whether there would be adults present, and whether alcohol would be there.
"It's responsible parenting. You need to know all those things as a parent. It's amazing how many parents just drop them off at the door once they become teenagers.
"It's about having that communication with your child."
Whether or not the law was enforced would depend on how seriously it was taken, Mrs Paine said.
If your underage teen got drunk on alcohol from someone else, the first step should be dealing with it within the family, she said.
"As a responsible parent, the boundaries and consequences you have around your child from day dot are not going to be any different around alcohol as they get older.
"If our child has had alcohol and it's a family rule you are not allowed to drink before you are 18, the consequences would have to come down to the child in the first place."
Justice Minister Judith Collins told the Bay of Plenty Times Weekend the alcohol reforms will make it harder for young people to get alcohol and to get drunk.
"Taken together, the express permission and responsible supply rules send a strong signal to young people and adults, as well as providing a tool for police to intervene in unsupervised or poorly supervised parties, such as after-ball functions.
"If it's not your child, it's not your call."
