Advertisers offering jobs to backpackers are being told they must pay the minimum wage or risk prosecution.

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Last week, RNZ revealed a job website - Backpackerboard - was advertising roles below the $16.50 per hour minimum wage.

The website has since pulled all job ads below minimum wage and decided to keep a closer eye on the site.

However, labour inspectors are taking a closer look at adverts that don't offer the minimum wage.

Workers' advocate Chloe Ann-King named and shamed the ads on Facebook - describing the job market as the wild west for backpackers and temporary visitors.

Since the story went to air, Ms Ann-King and RNZ have received a steady stream of complaints about working conditions.

The minimum wage increased by 75 cents this year, and equates to $660 for a 40-hour week.

One German backpacker said she quit her farm job in Waikato last week because she was earning below the minimum wage.

"I was working at least 48 hours a week ... at least ... usually more ... and I still got the same $400 every week," she said.

She said her living conditions on the farm were a disgrace.

"No heating ... if I would have stayed during the winter it would have got really cold and I had a portaloo outside ... at least it had a flush ... so it was just a former garage with a little bit of firewood in there and a lot of mice and spiders," she said.

Another German backpacker, Lukas, got $60 for 10 hours work picking kiwifruit flowers in Katikati, in the Bay of Plenty.

"On my last day I just started in the morning to get like maybe four kilos ... five kilograms ... just for like four to five hours just to have a little bit of money because for me it was personally just a waste of time and waste of energy," he said.

He said he walked after a few days work with $200 in his pocket.

'Many don't actually realise what the minimum wage is'

Labour Inspectorate national manager Stu Lumsden said it had been giving employers who advertised a call, and he was shaking his head.

"Many don't actually realise what the minimum wage is ... which is quite surprising... I think one situation they said they'd been overseas and hadn't realised that it had changed," he said.

He said ignorance of the law was no excuse and prosecution was an option.

"If we find that minimum entitlements have been breached ... an individual is liable for a penalty up to $10,000 per breach ... and $20,000 per breach as a company," he said.

The First Union has been outspoken about migrant workers' rights.

Its general secretary Dennis Maga said employers, including in rural and remote areas, needed to be informed of the law and pay the minimum wage.

He said the country needed more labour inspectors doing random checks.

"We believe that there is a widespread exploitation and it will continue unless we step-up our investigation ... inspection ... and ensuring that employers - especially the employers actually employing less than 10 people - will be checked from time-to-time," he said.

Last week's Budget set aside $2.2 million each year for the next four years to hire more labour inspectors, the first step in the government's promise to double the number of inspectors to 110.

Mr Lumsden said the Labour Inspectorate was working with Immigration New Zealand to better inform backpackers and temporary visitors about pay and rights.

Meanwhile, Federated Farmers is calling for better education about the minimum wage in rural communities to make sure temporary workers are paid and treated fairly.

Federated Farmers vice-president Andrew Hoggard said the message clearly was not getting through to some.

There was no quick fix, he said.

"These things take time... I do see certainly a lot of farmers coming through now who do have the good staff experience forefront in their mind."