Unions NSW says it lodged the dispute in September, after MTS refused to pay more than nine months worth of allowances and leave loading, originally promised to 32 staff in the lead-up to a finalised employment agreement.

The group had begun work in July 2019, to help get new Metro North West train services up and running, and felt betrayed when their back-pay requests weren't fully honoured by MTS, Unions NSW says.

Each worker's bank balance is now on average $10,000 better off, after a union-led case lodged in Fair Work Australia resulted in a final payout of more than $330,000 (plus superannuation).

Unions NSW secretary Mark Morey said the workers took decisive action to protect their wages.

"This outcome shows the real benefits when union members come together to protect their pay and conditions. I am proud that action by unions was able to convince MTS to do the right thing by its staff" he said.

He added that the case was not isolated.

"As budgets tighten, we are seeing government agencies and businesses increasingly playing Scrooge with the pay and conditions of staff," he said.

Australian Associated Press