Large clusters of workers are still not being paid the minimum wage, despite raised awareness of employment rights among vulnerable migrant workers, an expert says.

The Ministry of Business, Innovation and Employment's labour inspectorate found 136 businesses across Auckland and Northland failed to pay workers the minimum wage over the past five years.

The breaches came in "bundles" and affected large groups of workers, regional manager David Milne said.

123rf The Labour Inspectorate said the most minimum wage dispute claims came from retail and hospitality companies (file photo).

"Migrant exploitation still continues to be a strong focus for the Labour Inspectorate."

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There was also a growing awareness of employment rights among migrant workers, leading to a "noted increase" in the number of people making minimum wage complaints, Milne said.

Education provided by employment services had been "pivotal" in raising that awareness, he said.

"Correspondingly, there are more workers, migrants as well, with more dispute resolutions."

In 2018, there were 599 enforcement investigations conducted, leading to 4601 mediations. Of those, 76 per cent – 3451 cases – were closed.

Only 14 organisations of the 136 had to pay a penalty, which ranged from $145,000 to $200,000.

Among those were a North Shore food court which was fined $164,397 for forcing its Chinese migrant employees to work without pay for 20 hours a week and the Indian restaurant managers who served home detention sentences for paying staff less than $3 per hour.

Milne said investigations were becoming more and more complex and were more likely to feature "serious" exploitation.

"This means one complaint can amplify quickly as investigations dig deeper into the system."

The most complaints came from retail and hospitality companies, but also came from agricultural, cleaning and health industries.

Milne said his advice for people who felt they were being underpaid was to keep their own records. They should note hours and dates and reconcile pay against pay slips, he said.

"Self records for a worker can help with an investigation. If an employer hasn't kept records, that's an area we will penalise."

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* The numbers provided are for closed cases only and do not include cases that are still under investigation, involved in enforcement or in a monitoring phase with regard to compliance.