The Inspectorate found while the train engineers were working in New Zealand they were still employed by the Chinese company.
The workers and company failed to disclose their pay and working conditions to the Inspectorate because of privacy reasons.
The RMTU wanted the case to go straight to the Employment Court, where it could be decided whether or not foreign workers are subject to New Zealand employment law.
In the ERA's decision, the RMTU said KiwiRail outsourced work that could have been done by union members.
It also argued KiwiRail needed to comply with its obligations of good faith and social responsibility, and desist from "utilising exploited foreign workers, or proceeding in reckless disregard as to whether those workers are exploited".
KiwiRail asserted the Chinese workers were not employed by its company, and therefore the matter was going to be difficult to pursue under the Employment Relations Act.
The matter will be heard in the ERA tribunal, unless RMTU seeks special leave from the Employment Court for the matter to be heard there.
See the ERA decision here: