New Zealand's Labour party and the rail workers' union are demanding answers to claims Chinese workers brought to the country to fix asbestos-contaminated locomotives were paid as little as $NZ3 ($A2.79) an hour.

Labour’s Hutt South MP Trevor Mallard and the Rail and Maritime Transport Union say they have written to the Ministry of Business, Innovation and Enterprise asking for an urgent probe into the allegations.

The Chinese engineers were brought to New Zealand to remedy asbestos found in Chinese-made locomotives. The work was done at KiwiRail’s Lower Hutt workshops.

“My understanding is that a number of Chinese railway engineers dealing with the asbestos issue are being paid well below the minimum wage,” Mr Mallard said.

“The figure quoted to me was $NZ3 per hour but I have also heard $US40 ($NZ47.16) per day.

The ministry says it has received information and is making inquiries.

Forty DL locomotives, bought in 2010, needed to be taken out of service earlier this year after asbestos was found in soundproofing material.

The RMTU says the purchase of overseas rolling stock has been a sorry tale and the underpaying allegations needed to be investigated quickly.

Chinese staff were also working in Picton doing remedial work on the flat deck wagons, again under warranty.

“Again we’re hearing horror stories about the terms under which they are working,” said acting general secretary Todd Valster.

KiwiRail says the workers were employed by Chinese locomotive makers CNR and it was not privy to wage arrangements.

However, it took contractors’ welfare seriously and would be investigating. It would co-operate with any ministry inquiry, it said in a statement.

CNR could not be immediately contacted for comment.

The union says the rolling stock should have been built at Dunedin’s Hillside workshops, which have since closed because of a lack of work.

But KiwiRail says the last locomotive made in New Zealand was in the late 1950s and was steam-powered.

New Zealand didn’t have the capability to produce enough new locomotives quickly enough, it said.