"I have no idea when I'll be told what shifts I've got - it changes every week," says Caspian Okazaki, a Brighton-based assistant at a shoe shop.
"The shortest notice has been the night before, I was told at 9pm to come in an hour earlier for a delivery they were expecting."
He is among the 37% of working adults in the UK who are given less than a week's notice of their working hours, according to a study by the Living Wage Foundation.
The issue affects both full and part-time employed staff. That includes 48% of workers in London, and up to 35% of workers in other parts of the country.
It said 7% of working adults are given less than 24 hours' notice.
The Living Wage Foundation surveyed more than 4,000 people in order to understand more about how uncertainty over hours and work-schedule notice periods are affecting the UK labour market and people's livelihoods.
It also found that full-time workers being paid less than the £9.50 an hour real living wage were particularly hard hit by short notice of working hours. The thinktank said the problem affects more than two thirds of people from black, Asian and minority ethnic backgrounds, and 64% of people with children.
'Pressured to work'
"Because there's only a certain amount of staff in the store, if you don't do it, there's no one else who can do it, so you feel obliged to cover the shift at short notice," says Mr Okazaki.
"One time I needed my wisdom teeth out and I needed a week off, and they said no, I was only allowed to have three days off, so I had to come to work with a swollen face and migraines."
Mr Okazaki has worked for the same retailer for more than five years. He typically works between 16 and 25 hours a week, paid at minimum wage, and the days off change each week.
This became a problem during the pandemic because he was furloughed, receiving only 80% of his wages for a 20-hour week - the average of his working hours over the past 12 months.
"It is definitely not enough to live on if I didn't have a secondary income," says Mr Okazaki, an Instagram influencer who also owns an online alternative fashion apparel brand.
"If it wasn't for my brand, I would not have been able to pay my bills and rent and buy groceries through the pandemic."
The Living Wage Foundation is encouraging firms to sign up to its living hours pledge, which requires employers to both pay a real living wage and commit to providing at least four weeks' notice for every shift, with guaranteed payments if shifts are cancelled within this notice period.
It says insurers Aviva and Standard Life Aberdeen, as well as Scottish energy provider SSE, have so far signed up, committing to provide workers with secure, guaranteed working hours.
"Without clear notice of shift patterns provided in good time, millions of workers have had to make impossible choices on childcare, transport and other important aspects of family life," said the Living Wage Foundation's director Laura Gardiner.
"Low-paid workers have been particularly hard hit during the pandemic, with millions struggling to plan their lives due to the double whammy of changing restrictions on economic activity and insufficient notice of work schedules from employers."
The government said it had consulted on the issue and was analysing the results in light of the impacts of the Covid pandemic on the labour market.
The consultation included proposals on providing reasonable notice of shifts and providing compensation for shifts cancelled at short notice.
A spokeswoman for the Department for Business, Energy & Industrial Strategy said: "We are determined to tackle unfair working practices, while ensuring that everyone can enjoy the benefits of flexible working patterns.
"The government has consulted on introducing compensation for short-notice shift cancellations and a right to reasonable notice of shifts. We are analysing these responses, and will respond in due course."