A third of young workers miss out on superannuation because of an “unfair” rule dating back to the 1990s, an expert has warned.

It is the key finding of an upcoming report by the John Curtin Research Centre and Vision Super, due in September.

Currently, bosses don’t have to pay any superannuation at all if their worker earns less than $450 a month.

Overtime doesn’t count towards the threshold, and it applies to each employer separately – so a worker with two jobs that each pay $400 a month in ordinary earnings and $200 a month in overtime still misses out on compulsory super.

The report’s author, Dr Nick Dyrenfurth, executive director at the Curtin centre, said the “arbitrary threshold” punishes young people, especially women who are more likely to be casuals.

“It’s not only unfair for young and often female employees, but it’s actually a policy problem that needs to be taken seriously by policy makers on a national scale,” he told The New Daily.

“If people aren’t accruing super, that’s going to place enormous structural pressure on the budget and our retirement savings system if we don’t take action now.”

An estimated 220,000 Australian women and 145,000 men miss out on about $125 million of super a year because of the rule, according to the Association of Superannuation Funds of Australia.

Dr Dyrenfurth warned the rise of the “gig economy” would push even more young workers beneath the threshold, as their earnings get split between employers.

“The system of compulsory super built up from the early 1990s has been a national and really a world-beating success story. We built up one of the largest pools of savings in the world in just over a quarter of a century – the largest in Asia and the largest per capita in the world,” he said.

“But the labour market and the economy around which the system was first built – traditional 9-to-5, full-time jobs where people work for one employer for at least a decade – has really disappeared in favour of the ‘gig economy’ dominated by part-timers and casuals.”

New official data has confirmed sideline gigs are rising.

Over the past six years, the number of Australians with secondary jobs increased 9.2 per cent (from 699,000 in 2010-11 to 763,000 in 2015-16), while Australians with main jobs rose by only 6.8 per cent (from 11.7 million to 12.5 million), the Australian Bureau of Statistics reported on Tuesday.

Mr Dyrenfurth noted the government’s newly announced regulations for the superannuation industry did not include any action on the $450 threshold.

“Just as young employees can often see retirement as being a long way off, so too governments of all stripes need to keep one eye focussed on the future.”

Reducing or abolishing the $450 threshold was a key recommendation of a recent report from The Australia Institute, which warned the retirement system is failing women.

A Senate committee chaired by Labor recommended in May that it be scrapped. The inquiry’s Liberal deputy chair, Senator Jane Hume, has also backed the reform.

Many interest groups, including Industry Super Australia, Anglicare, the National Foundation for Australian Women, Women in Super and the CFMEU, made submissions to the inquiry agreeing it should be abolished.

The rule is widely misunderstood. A survey of 1059 employees by Longergen Research in 2016, commissioned by industry fund REST, found that 47 per cent of casuals and 40 per cent of part-timers thought they were paid super from the first dollar they earned.

Dr Dyrenfurth’s final report will also recommend that employers pay their workers more superannuation, and advocate more government funding for financial literacy.