A lobby group campaigning for the repeal of anti-smacking legislation has released survey findings showing many parents are confused about the law change.

In research commissioned by Family First NZ, respondents were asked whether the new law made it always illegal for parents to give their children a light smack.

As the law stands there are some circumstances where a light smack would not be illegal.

Fifty-five per cent of the 1000 people surveyed thought smacking was always illegal, 31 per cent thought it was not, and 14 per cent did not know.

"This proves just how confusing the law is to parents and it is this confusion that is causing huge harm," said Family First national director Bob McCoskrie.

To add to the confusion, a survey undertaken by the Office of the Children's Commissioner in November last year found that 43 per cent of those surveyed who knew of the law change supported it.

"Only 28 per cent were opposed to the law change. The remainder were neutral," Commissioner Cindy Kiro said.

The survey was conducted as part of efforts to judge public opinion in the lead-up to a referendum taking place in August this year on the 22-month-old law, which removed the defence of reasonable force for disciplining a child.