Apprentice tradespeople across Queensland could be in line for a windfall after a court ruled an industrial loophole left them underpaid for almost four years.

The Federal Court in Brisbane ended a long-running wages dispute on Monday by finding more than 4,000 trainee electricians were short-changed under an expired state award that paid them less than $9 an hour.

The ruling means thousands more apprentices, from trainee hairdressers to plumbers and butchers, can now mount lost wage claims because they should have been paid under federal awards.

Electrical apprentice Reuben Weston said the ruling was "great". ( Facebook: Reuben Weston )

The Electrical Trades Union told the ABC this could amount to backpay claims totalling between $100 and $200 million.

Apprentice electrician Reuben Weston said he stood to gain more than $7,000 in backpay after being underpaid for two years.

"It's absolutely great because as we know now that we were underpaid for that amount of years, it'll help me very much financially," he told the ABC.

"From what I've been told [the repayment] could be as early as January.

"They're just going to try and pump it as quick as they can because there are thousands of us who were underpaid."

ETU Queensland apprentice officer Scott Reichman said the ruling made clear that payments under an outdated state award were "always illegal, and means we can seek wage justice for these young people".

Mr Reichman said trainees who had fallen victim to "broken workplace laws" from the start of 2014 would in the electrical sector alone press for more than $70 million in underpayments.

Master Builders 'concerned for employers'

The wages battle began in 2015 when the Fair Work Commission found an apprentice agreement by All Trades Queensland should reflect a modern federal award of $13.07 an hour rather than an expired state award of $8.75.

That ruling set the federal award as the minimum standard for apprentice pay.

However, All Trades Queensland — which bills itself as Australia's largest commercial supplier of apprentices and uses rugby league star Cameron Smith in its advertisements — appealed before the full bench of the commission.

The commission upheld the ruling.

All Trades Queensland, the Housing Industry Association and Master Builders Queensland then applied to have the Federal Court strike down the ruling.

The Federal Court found Queensland apprentices must be paid under federal awards. ( ABC News )

Master Builders Queensland deputy CEO Paul Bidwell said the decision affected "carpenters, bricklayers, plasterers, painters", but went far beyond the building industry.

"Our concern is what will the impact be on the individual businesses and the group training schemes who employ the lion's share of apprentices," Mr Bidwell told the ABC.

"What's it going to mean for them for the future?"

Mr Bidwell said Master Builders had "no real sense" of the total cost to employers from backpay claims.

"It's more from our perspective about what's going to happen into the future and to make sure that those businesses … are in a position to keep on employing apprentices," he said.

Mr Bidwell said it was too early to know whether the ruling would trigger an apprentice hiring freeze, with the transition to higher wages yet to be settled with a state election just gone.

"It's premature to say anything really, until we've got a government in Queensland, and we can have conversation with them, as well as the Federal Government."

Mr Bidwell rejected any suggestion some employers had rorted their apprentices, saying the ruling on the higher wages by the commission in 2016 "came as a complete surprise" to businesses advised by governments and workplace authorities they had been doing the right thing.