Backers of shorter working weeks have reacted with scepticism after Bunnings Warehouse announced it would back a four-day trial for thousands of its staff.

Some 40,000 Bunnings workers will trial the shorter week, under a landmark agreement with the Shop Distributive and Allied Employees Association.

It will allow Bunnings staff to work 38 hours across four days, or spread their hours out in a nine-day fortnight.

They will also get a 10.5 per cent pay rise over the next three years, the retail giant said.

SDA delegates endorsed the deal last week, saying it could set a precedent for retailers. National secretary Gerard Dwyer said it was a “significant breakthrough” in work-life balance for retail workers.

“These are advances the SDA will be pursuing in upcoming rounds of negotiation with other major retailers,” he told the Australian Financial Review.

“This package is good for workers and for this major retailer alike, setting Bunnings up as a preferred employer in a tight retail market.”

Under the agreement, the workers will also be entitled to five weeks of annual leave.

The company’s chief people officer, Damian Zahra, said the deal would also change Bunnings’ approach to days in lieu relating to public holidays.

“We have a track record of providing industry-leading pay, benefits and bonuses, and our aim is to provide a new EA that continues to reward our team for the great work they do every day,” Mr Zahra said.

The deal will be submitted to the Fair Work Commission for approval, after workers vote on it.

But 4 Day Week Australia, a major proponent of the trend towards shorter working weeks, said the Bunnings deal was really a “compressed work week”.

“We applaud Bunnings for supporting its staff with flexibility. But introducing a compressed working week, rather than reducing hours, is a missed opportunity,” the organisation’s campaign co-director, Adrian McMahon, said on Monday.

“Around the world, the four-day week, with reduced hours and no loss in pay, is leading to exceptional results for worker health and wellbeing and company productivity. With so many benefits on offer, we encourage Bunnings to recognise that reduced hours are just the beginning.”

The organisation cited a growing body of international research that showed a four-day week had international support because of the benefits to health and wellbeing, productivity, gender equity and the environment.

The concept has recently been trialled in several Australian companies, including an accounting firm on the Sunshine Coast, a marketing agency in Melbourne, a consultancy in Darwin and property managers in Perth.

Earlier this year, charity Oxfam signed up to a four-day week for its 100 Australian workers.

Unilever – maker of household staples such as Dove, Rexona, Surf, Persil, TRESemmé, Continental and Streets – this year extended a trial of a four-day week to its Australian workers after a successful test over 18 months in New Zealand.

“As part of the initiative, staff retain 100 per cent of salaries, while working 80 per cent of the time, while still committing to 100 per cent delivery for the business (100:100:80),” Unilever said in announcing the Australian trial.

The Senate Select Committee on Work and Care has also backed a trial of a four-day working week for the public service. It said it would “make employment more accessible, [and] encourage the creation of more jobs for people”.

Citing dozens of international studies, the committee found evidence showed that the four-day week works.

For example, a study by Boston College, the University of Dublin and Cambridge University researchers last year tracked 33 companies that implemented a four-day week. Most simply allowed the majority of their staff to take Fridays off, while some let workers choose.

The results were overwhelmingly positive, with companies hailing the overall effect on their workplaces, including a beneficial effect on productivity.

More than nine in 10 of those involved said they either planned to or had already said they would continue the four-day weeks. No employer stopped it entirely.

“On average, company revenues increased more than a percentage point a month during the trial,” the researchers wrote in their report about companies’ experience with a four-day week.

In April, 4 Day Week Australia launched a petition asking the Australian community to support its push for a government-supported trial. It can be found here.