National training institute Te Pūkenga is refunding more than $500,000 in fees to plumbing, gasfitting and drainlaying apprentices.
The repayment follows a successful challenge to a fee rise earlier this year.
Te Pūkenga told RNZ it was refunding about 2400 learners between $224 and $286 each "as a result of fee reductions".
Master Plumbers told its members the refund reversed a $5 a week fee (or 4 percent) increase, which was introduced in February after the institute took over the apprentices' training and assessment.
"At the start of 2023, Master Plumbers challenged Te Pūkenga on its decision to increase fees for all PGD trainees, from $54 a week to $59. Over a full year, this is a significant amount for apprentices working on training wages, on top of inflation and the cost-of-living increases," it said in a message to its members.
Master Plumbers chief executive Greg Wallace told RNZ that both apprentices and employers were grateful for the change.
"It's a significant amount. You know for our apprentices most of them are on minimum wage or a training wage, that's actually a lot of money for them and we think it was important to advocate for them," he said.
Wallace said the fee increase breached apprentices' training agreements, which had been transferred unchanged to the new organisation.
"We strongly advocated for both our apprentices and our business owners to make sure that the terms and conditions of the contract they signed up with, which was originally Skills, an ITO [industry training organisation], were enforced," he said.
Te Pūkenga said it also took over training agreements for learners in other fields, but they would not get refunds because the terms and conditions of their training agreements were different.