ASDA has scrapped its four-day working week after staff complained the system left them feeling exhausted.
Last year, the supermarket started a trial of flexible working hours for managers, but the reduced hours were rejected by employees.
Employees in the trial at 20 Asda stores worked 44 hours over four days instead of five for the same pay.
However, workers said the 11-hour shifts were “physically demanding” and left them exhausted on their extra day off.
It comes as Britain’s largest trade union, Unison — one of Labour’s biggest funders — prepares to lobby the new government to introduce a four-day working week.
Labor advisers have played down the idea of introducing legislation for a shorter working week, despite the union formally backing the idea.
Unison was among the donors who handed Labour large sums of money in the run-up to the election, with more than £150,000 going to the party.
In addition to exhaustion, Asda workers also struggled with starting early and finishing late despite working four days a week.
This particularly affected employees who relied on public transport to travel to work.
Parents said the longer days made it more difficult to take children to and from school.
In response, Asda has halted the pilot and cancelled a nine-day, two-week trial period.
The grocer is still testing a working pattern that sees workers work 39 hours a day, spread over five days (equating to shifts of just under eight hours) without taking a cut in pay.
Asda said this has proven more popular – some employees who previously tried the four-day week asked to switch sooner – and that it will last until the end of 2024.
A pilot project will also be continued with a new retail structure, with additional payroll managers being hired in some departments.
An Asda spokesperson said: ‘Last year we started testing four different flexible working patterns for managers across 20 stores.
‘In April we announced that two of these trials, a new store structure and five shorter working days, would run until the end of the year, after receiving positive feedback from colleagues in these stores.
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‘We continue to trial different flexible working patterns to assess how they can benefit our colleagues and our business.’
Other companies are also turning against the idea of a four-day workweek, fearing that employees will not be able to cope with the longer working days.
Appliance specialist Domestic & General has halted its four-day working week trial after staff felt “mentally” exhausted.
Matthew Crummack, CEO of D&G, told the Daily Telegraph: ‘Half the team loved it, the other half hated it. It makes the day last longer and a bit more intense.’
The company will be trialling ‘school hours’, allowing parents to work between 9:30am and 2:30pm.
Last year, a London tech company scrapped plans for a four-day working week after discovering it would further stress staff.
Internet service provider Krystal has stopped the trial because colleagues were struggling to complete all their tasks in the limited time.
Krystal then shortened the workday from six to five hours.
The pandemic has seen more employees working from home and adopting more flexible working hours instead of the usual nine-to-five, five-day workweek.
Some economists argue that working fewer hours would lower living standards.
Critics say the concept is impossible in jobs that involve direct customer contact or 24/7 operations, where overtime pay adds costs to employers or taxpayers.