The Department of Labour has investigated 239 claims of underpayment in the Bay of Plenty's horticultural sector over the past five years.
The Department says claims of underpayment have risen as horticultural workers became more aware of their rights through contact with seasonal workers from the Pacific.
As a result of the investigations, underpaid workers were paid their outstanding wages in 41 per cent of the cases and employers were able to comply with the law without paying any extra in a further 14 per cent of cases.
The Department of Labour, now known as the Labour Group within the Ministry of Business, Innovation and Employment, found 3 per cent of the claims to be unsubstantiated while 5 per cent of claims were withdrawn by the claimants.
The Labour Group was forced to cease its investigation in 37 per cent of cases (88 complaints) because the employer had gone broke, left the area or the complaining employee could no longer be contacted.
In most of the cases where the Labour Group found the employer to be at fault, the employer accepted the findings of the labour inspector and voluntarily complied with a repayment plan.
However, in seven cases the labour inspector was forced to use enforcement actions to get the employer to comply with the law.
In previous years this required taking the employer to the Employment Relations Authority, but legislative changes in May last year gave labour inspectors new tools called enforceable undertakings and improvement notices.
Since then six Western Bay employers have entered into enforceable undertakings to review their remuneration records and pay any arrears, in some cases to all employees past and present.
Paying below the minimum wage and/or not paying annual holidays or public holidays were the common breaches of law that prompted the Labour Group to act.
Official complaints (according to Ministry data) stayed low until 2009 then rose dramatically (from 3.2 complaints per 1000 employees in 2008 to 19.1 in 2009) and stayed high during 2010 (22.8) and 2011 (17.2).
A Labour Group spokesperson said the rise is thought to be a "knock on effect" of the first phase of the Recognised Seasonal Employment (RSE) scheme.
"Contact with RSE workers is thought to have led to increasing awareness of worker rights amongst the general workforce in regard to minimum standards which in turn led to an increase in the number of complaints."
New Zealand Kiwifruit Growers president Neil Trebilco said that although there was no direct link between the grower and an orchard contractor's employee, they were disappointed whenever contractors underpaid staff because it reflected poorly on the whole industry.
However, putting the problem into context, he said the kiwifruit industry employed about 9000 seasonal workers in the Bay each season - and the 239 claims represented five seasons.
"It is not a large problem.
"Generally the contractors are pretty good, but human nature being what it is, there is always going to be someone who will bend the rules."
Mr Trebilco said the contractors who bent the rules were often the ones who did not last long in the industry.
Horticulture New Zealand spokeswoman Leigh Catley said underpayment was not a common problem in the industry and she did not believe it was getting any worse.
She said the Recognised Seasonal Employer programme had made the industry more productive and created more jobs for New Zealanders as well as Pacific Islanders.
"So employers are giving all workers more job security and more employment, and people who are moving around from employer to employer can recognise when industry standards aren't being met, and they are able to complain.
"Also more Kiwis have been interested in working in horticulture since the RSE scheme gave the industry good publicity about job availability. New Zealanders who get new jobs in horticulture and then find themselves being incorrectly compensated will either complain, or go and work somewhere else in horticulture where they will be looked after better."