Around four and a half million people are in work which is insecure, such as zero-hours contracts, a new study has revealed.
Research by Citizens Advice highlighted the scale of the issue in England and Wales, which the charity said was presenting huge numbers of workers with challenges in planning their finances.
Over 2.3 million people are working variable shift patterns, 1.1 million are on temporary contracts and 800,000 are on zero-hours or agency contracts, it was found.
A survey of over 2,000 adults for Citizens Advice found that most rated a steady, reliable income as important as how much they were paid.
More than four out of five of those polled said a steady job with regular pay rises led to increased productivity and loyalty towards employers.
Citizens Advice said there was an urgent need to improve security at work.
Chief executive Gillian Guy said: "Income security is the overlooked piece of the labour market puzzle.
"While for some people working shifts or temporary contracts may provide the flexibility they want, many others struggle to balance the books in the face of such insecure employment.
"We've found that when people are looking for work, getting a steady income is just as important to them as what they'll be paid.
"Having a steady, reliable income is fundamental to how secure people feel and is key if the Government wants to achieve its ambition of a high wage, low welfare economy.
"Offering people a secure income is also in the interest of employers, as it boosts staff morale and productivity.
A 22-year-old care worker who contacted Citizens Advice for help, described the challenges she faced in insecure work, saying: "I worked anything from 12-50 hours each week.
"Not having set hours was really difficult as some weeks I did not have enough money to cover my bills or rent. I never knew how much money I would have so I could never budget or plan ahead."