Transport Minister Gerry Brownlee has been forced to defend KiwiRail in Parliament after the discovery of asbestos in newly purchased Chinese locomotives.
Mr Brownlee summoned KiwiRail's management team to the Beehive on Tuesday for a "please explain" and later told the House he has full confidence in the state-owned company.
The Rail and Maritime Union says initial tests show KiwiRail workers could have been exposed to potentially lethal amounts of asbestos.
KiwiRail pulled all 40 engines out of service on 27 February after it discovered the highly toxic material had been sprayed on parts of the locomotives.
During Question Time on Tuesday, Labour Party MP Darien Fenton asked Gerry Brownlee whether he had confidence in the company, given the finding.
The minister replied yes, and said KiwiRail specified in its contract with the Chinese manufacturers that no asbestos was to be used.
Mr Brownlee said the company would not resume using those locomotives until it is completely satisfied that there is no health risk to its employees and the public.
KiwiRail has yet to release the results of testing it has been carrying out, but union secretary Wayne Butson said initial results showed members could have been exposed.
Mr Butson said one of the inspectors told him on Monday the resin sealing in the asbestos was being corroded by heat, and up to four of the locomotives were in a parlous state.
He said he was told at least two engines should be parked up permanently to prevent workers coming into any further contact with the degraded asbestos.
Final tests on the locomotives are due back on Tuesday.