A year-long investigation by authorities found kiwifruit contractor Aulack​ failed to pay correct pay to four workers.

A Bay of Plenty kiwifruit picking business has been fined and ordered to pay more than $30,000 for avoiding minimum wages and illegally deducting money from a worker.

A year-long investigation by the Labour Inspectorate found Aulack​ Enterprises failed to correctly pay four workers.

Aulack made 12 employment breaches, mostly relating to employment agreements and wage record-keeping.

The Employment Relations Authority (ERA) said Aulack was a repeat offender as it had previously been issued a notice by a labour inspector in 2014.

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That notice was resolved when the company's director, Hardeep Singh, provided a month's worth of timesheets and talked with an inspector about its minimum wage obligations.

The recent investigation found Aulack failed to pay the minimum wage to two employees, made unauthorised deductions from one employee's wages and did not provide holiday pay to another.

The inspector's inquiry began with a request for a sample of records for five workers but, after speaking with other workers, found the identified breaches were only the tip of the iceberg.

A statement taken from a senior employee, who was in charge of payroll and involved in other administration, disclosed systematic underpaying of workers, the ERA said.

The inspectorate found more than 250 people had worked for the business in the 12 months previous to its inquiries.

Most were backpackers on working holiday visas and locals who were transient or casual.

They were employees vulnerable to exploitation because they were less able to identify the employment breaches, the ERA said.

Aulack has been ordered to pay the inspectorate $10,000 on behalf of employees, $20,000 for breaches of employment standards and a further $2000 in costs.

Labour Inspectorate regional manager Kevin Finnegan​ said although the whole sum owed to employees was about $500, the "persistent and deliberate" breaches have meant a hefty $30,000 fine.

"This sends a strong signal to employers that where you repeatedly breach employment law, you will face serious consequences," Finnegan said.