A group of overseas students, who paid thousands to come to New Zealand to complete internships, say they're being "treated like slaves".

The hotel management students are cleaning rooms at a flash hotel and claim they've been underpaid, overworked and, if they complain, threatened with deportation.

The students paid up to $6000 each to Wellington company Internship New Zealand to come here to gain international experience.

They were then employed as housekeepers by cleaning company AHS, which services rooms at the Grand Mercure in Wellington.

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They thought it would be a life-changing experience. But instead the students say they were instructed to alter their time sheets so some of their hours are not being paid, and unfairly docked their pay.

"We are treated like slaves - not like employees - so that's what hurts me," one told Newshub.

One worker who failed to correctly tidy a room was phoned up and abused by the Internship NZ boss. She called him a "lazy-ass idiot" and told him if it continued, he would be sent home. Newshub has obtained a recording of that phone conversation.

"Well, lift your f**king finger out of you-know-where and work as expected," Internship NZ managing director Karen Oswald says in the recording.

"You don't get to work like an idiot - lazy-ass idiot - and then have no consequences."

She even threatens to have the worker kicked out of the country.

"And I tell you - I don't put up with this rubbish - you will be going home," she told them.

Newshub has learned she is a former employee of the Department of Labour, which is now known as the Ministry of Business, Innovation and Employment (MBIE) - the very agency charged with fighting worker exploitation.

Newshub called Ms Oswald, who happened to be in India recruiting more interns. She attempted to justify her actions.

"Sometimes you need to be kind to them, and sometimes you just want to put it in perspective for them," she told Newshub.

Cleaning company AHS is also accused of exploitative behaviour. Workers told Newshub AHS management instructed them to write earlier finish times in the time sheets and claim they've been cheated out of wages.

Unite Union national secretary Gerard Hehir says that's illegal.

"[It's] basically stealing their wages. And because these workers are all on minimum wage, that immediately means that if they work unpaid hours, they're getting less than the minimum wage," he says.

Genie Dhariwal confirmed AHS has been telling workers to enter different finish times.

He should know - he's a current supervisor with AHS, and says he was also instructed by his manager to alter the time sheets of workers.

"At the beginning, when I came in, I felt that this was wrong as I had been working in the industry for three years now. And I hadn't experienced it anywhere before, but I was told to do the same," he told Newshub.

Newshub wanted to know more about AHS's links with Internship NZ. When we asked, AHS told us that the business relationship is now over. Two senior AHS managers have flown here from Australia to investigate.

Accor Hotel group, which owns Grand Mercure, says it prides itself on treating employees fairly and with respect. It's also investigating.

Newshub.