The Mana Party is comparing a lower wage for some 16 to 19 year olds with slave labour.
The Government is to introduce legislation that would allow employers to pay 80% of the minimum wage, or $10.80 to some teenage workers for the first six months in a new job.
Workers aged 16 and 17 can already be paid the lower wage for three months.
The Minimum Wage (Starting-out Wage) Amendment Bill extends that to the first six months of a new job, and includes 18- and 19-year-olds who have been on a benefit. It will also apply to all those aged 16 to 19 who are in industry training courses.
The Government says it will encourage employers to take on inexperienced job seekers.
Business New Zealand says it will help young Maori and Pacifica workers who have few skills into their first jobs, but the Council of Trade Unions says the jobs aren't there.
The Mana Party says the minimum wage is hard enough to live on, and reducing it would prompt more young people to head to Australia.
It says money-hungry businesses might lay off older staff to take on younger, cheaper workers.