Key Points:

Workers aged 16 and 17 will earn the adult minimum wage once they have been in the job three months or worked 200 hours under a law change yesterday.

Currently, those under 18 must be paid 80 per cent of the adult minimum wage. But that will change from April 1 after Green MP Sue Bradford's Minimum Wage (New Entrants) Amendment Bill was passed.

Labour, New Zealand First, United Future, the Progressive Party and independent MP Taito Phillip Field voted with the Greens' six MPs to pass Ms Bradford's bill.

National, the Maori Party, ACT and independent MP Gordon Copeland voted against the legislation.

Ms Bradford said she had introduced the legislation because young workers had been underpaid and undervalued.

It was unfair that 16- and 17-year-old workers were paid less for doing the same job "simply because of their age".

She had originally drafted the legislation to scrap youth rates.

But it was amended - to gain enough political support to get it passed - so that 16- and 17-year-old workers would get the adult minimum rate after 200 hours or three months work, whichever was the shorter. Employees supervising or training other workers would be paid the adult rate.

Ms Bradford said she could live with the compromise because it marked a huge improvement.

Maori Party MP Te Ururoa Flavell said his party had supported the original version on the bill, not the compromise which discriminated against young people. Half the 16- and 17-year olds working did 10 hours or less work per week, Mr Flavell said.

This meant that under the bill's provisions it would be five or six months before young people were considered worthy of earning the basic minimum wage, he said.

National MP Kate Wilkinson said her party was concerned a higher pay rate might prompt young people to quit school early to start working. The legislation could also be counterproductive, pitting young people with little work experience against those with many years' work experience.

"What employers don't want is to be forced to pay a young person the same as an older person when they're not providing the same value."

Labour Minister Ruth Dyson said: "Labour recognises that often employees who are aged 16 or 17 do the same work as adults - but we also recognise that time is needed for those workers to gain the socialisation skills needed for working."

When the law changes next year the youth minimum age rate, currently $9 an hour, will be replaced by the "new entrants' minimum wage".

Ms Dyson said the actual rate would depend on the minimum wage review which was already under way.

If economic conditions allowed and the Government was able to move the adult minimum wage to $12 an hour before the end of this parliamentary term, the new entrants' minimum wage would rise to $9.60 an hour - or 80 per cent of the adult minimum wage.

On April 1 this year, the minimum wage rose to $11.25 an hour.

Ms Dyson said the increase in the youth minimum wage rate over past years had had a "neglible impact" on the number of young people leaving school early.