The union for rail workers is taking KiwiRail to court over its use of Chinese workers.
Dozens of the workers are being used to repair faulty diesel DL locomotives. The trains are riddled with asbestos and were imported from China in 2010.
Rail and Maritime Transport Union (RMTU) spokesperson Todd Valster says not using New Zealanders for the job is a breach of good faith and KiwiRail's social responsibilities.
"We're more concerned about the work returning to the KiwiRail employees who are mechanical engineers who can take the trains apart and put the trains back together again and we just can't see that in sight, maybe we could have Chinese workers for up to 25 years going by what KiwiRail's saying and we just think that's unacceptable."
Mr Valster says the union's also concerned over how the foreign workers are being treated.
"Our union has made repeated attempts to determine whether the workers from CNR are receiving minimum entitlements like the pay rates in our collective agreement or even the New Zealand minimum wage."
"This problem never would have emerged if KiwiRail employed its own workers to do the repairs and reconstruction. RMTU members have done similar work in the past."
KiwiRail says it doesn't accept the union's version of events, or that it's breached its responsibilities as a state-owned enterprise.
It wouldn't comment further, saying the matter is currently before the Employment Relations Authority.
The hearing will take place before the ERA in Wellington until Thursday.