Union members won't be working on asbestos contaminated Kiwirail trains until all the material has been removed, the rail workers union says.
Some KiwiRail freight services have been cancelled after asbestos was found in a paint sample.
On Friday, the company said the substance was found in the soundproofing compound used in 40 DL locomotives, which have been grounded while testing is carried out.
KiwiRail doesn't expect final results until later on Monday, spokeswoman Jenni Austin says.
On Saturday, Rail and Maritime Transport Union general secretary Wayne Butson said members wouldn't be operating those trains until all asbestos has been removed.
"It's a death sentence," he told One News.
"The simple fact that we've got a locomotive, brand spanking new, made this century, is actually appalling to have this substance in it."
Analysis found the asbestos is contained and not a health risk but the company has notified all affected staff.
"Once testing is finished and we have a clearer picture of the situation, we will work with the manufacturers to rectify the situation," KiwiRail chief executive Peter Reidy said.
Kiwirail says some weekend services have been cancelled but other trains are being used to carry urgent freight.
"We have juggled services around a bit and made a few cancellations of less time sensitive freight over the weekend," she told NZ Newswire on Saturday.
The cancelled freight will go at a later time, she said.
It was fortunate freight loadings were quieter at the weekend and didn't pick up again until Monday night, Ms Austin said.
KiwiRail has 198 mainline freight and passenger locomotives, she said.
Passenger services are not impacted.
KiwiRail says the use of asbestos was a breach of contractual specifications for the design and manufacture of the locomotives.
"We are clearly very disappointed with this situation and are working closely with the manufacturers to understand how this could possibly have occurred," Mr Reidy said.
"They have taken full responsibility for this and have undertaken to do whatever is necessary to rectify the situation as quickly as possible for us."
The locomotives were built by Chinese company Dalian Locomotive and Rolling Stock Co.
KiwiRail says it sought and received assurances that no asbestos was used in the making of the locomotives from the manufacturer in 2013, following reports of asbestos in Chinese-manufactured locomotives in Australia.
Labour says cost cutting is to blame for the problems.
"Lowest cost tendering, cuts to rail maintenance and contracting-out have led to a catalogue of problems," Labour transport spokesman Darien Fenton said.
"This is taking a toll on our Kiwi-owned rail company."