When one of Western Australia's largest aged care providers admitted to underpaying workers, Madeline Jones* thought she would receive thousands of dollars for hours of overtime she worked as a senior nurse.

Instead, the former Busselton Aegis employee has been promised nothing.

"I did hours of overtime for that company," she said

"I remember on several occasions doing a Saturday, Sunday, Monday and working from seven in the morning to 11 at night … so those are very, very long hours to work and not be recognised for that.

The company, which operates 30 residences in Perth and the South West, claims the "historical" issue meant workers were paid casual loading instead of overtime pay. 

It would not be drawn on specific details around total payouts or the numbers of current and former staff impacted, but a spokesman said the average payments were "not significant".

This was countered by the United Workers Union, which said on its website that Aegis "rorting" had gone on for almost a decade and would likely amount to millions of dollars.

Under Australia's Fair Work Act, there is a six-year statutory limitation on underpayment claims, which means staff like Ms Jones, who left Aegis 12 months before the cut-off, will be paid nothing.

"I think it's a despicable act," she said

"They created that situation out of dishonesty, and it was only [discovered] because of a staff member. 

"Had this not come to light, the practice would probably still be continuing."

Ms Jones said the law should be overhauled to better protect workers like herself.

'Scot-free' after six years

WA lawyer John Hammond has worked on employment and industrial relations cases for more than 40 years.

He agreed six years was not enough time, because many employees did not realise a mistake had been made until years later.

"The industrial relations system in Australia is a complete mess," he said.

"I think the six-year period should be doubled, particularly in situations where there has been an intentional act to stop someone being paid their full salary."

He said underpayment issues were happening frequently across Australia and the system made it hard to recoup money.

"I think that's very unfair when you consider the work has been done."

Repayment beyond six years encouraged

The federal Department of Employment and Workplace Relations said the laws balanced employee rights and the public interest for disputes to be settled in a timely manner.

"A six-year time limit also recognises the fact that over time, evidence becomes more difficult to identify," a spokesman said.

"For example, the people involved may no longer work for the business or may have difficulty recalling events, and relevant records may become more difficult to locate."

The spokesman said companies were free to make their own choices about paying employees who left earlier.

Agreement struck with union

In a statement, an Aegis spokesperson said it had resolved the issue with the union.

The company said it had also launched a "comprehensive review" of its employee entitlements.

"We expect this process to be fully complete by October 31, after which Aegis will be contacting all affected employees," the spokesman said.

*Name changed for privacy reasons.