Low-paid workers are confused about what they should be paid and the types of deductions employers can take from their pay packets, a poll found.
Almost 70% of people earning less than £15,000 a year did not know they should be paid for travel time between appointments, while around half were unaware that tips cannot be used to top up pay to the legal minimum.
And 57% had no idea that money taken from their wages to pay for uniforms was against the law if it takes their earnings below the minimum wage or national living wage (NLW).
The study of 1,400 workers was carried out ahead of the launch of a national advertising campaign by the Government to help make sure low-paid workers are aware of their rights.
Increases to the minimum wage and NLW come into effect from April 1 and workers are being encouraged to check their pay, speak to bosses about the rate rise and report any underpayment to Acas, the workplace advice service.
Business minister Margot James said: "We are determined to make sure everybody in work receives a fair wage and while most employers get it right, there are still a small number who fail to play by the rules.
"This campaign will raise awareness among the lowest paid people in society about what they must legally receive.
"Anyone who thinks they may be paid less than the legal minimum should contact Acas as soon as possible."
The campaign, which will see posters on public transport and in shopping centres, highlights ways in which workers may be underpaid and encourages them to check their wage packets.
Excuses given to tax authorities by employers for underpaying workers include using tips to top up pay to the minimum wage and making staff pay for uniforms out of their salary.
Others refuse to pay staff for shutting up shops, time waiting for security checks or the time spent travelling between appointments.
Jennie Granger, from HMRC, said: "Paying the national minimum wage is the law - it's not a choice. Employers must pay their workers what they're entitled to and follow the rules.
"We will act to ensure ripped-off workers receive their proper pay and hard-working businesses are not losing out to dodgy dealers who cheat their staff."
Stewart Gee, head of guidance at Acas, said: "It is important for employers to stay within the law and for workers to be fully aware of the pay that they are legally entitled to."
For advice and to report underpayment, visit www.gov.uk/checkyourpay and www.acas.org.uk/nmw.
The NLW for those aged 25 and over will increase from April 1 by 30p, to £7.50 an hour.
The minimum wage for 21 to 24-year-olds will go up by 10p to £7.05, for those 18 to 20 by 5p to £5.60, and for 16 and 17-year-olds by 5p to £4.05.
Apprentices will see their minimum wage rise by 10p to £3.50 an hour.
:: Populus carried out a poll of 1,435 UK adults aged 16 and over and earning less than £15,000 a year, questioning them between February 14 and 20.