Martin Lewis is telling Brits that half a million of us on minimum wage might be underpaid - and how to get your more money if you are owed anything.
The MoneySavingExpert founder said workers could be underpaid if they are required to buy items to do their jobs, like safety clothing or tools.
Other people who could be eligible are underpaid because they have unpaid working time, such as having to get to work early to open the premises.
Employees who get minimum wage should also get a pay increase from April every year under law.
From this April the hourly rate for earners aged 21-22 is £9.18 an hour, up from £8.36.
Minimum wage is officially called the National Living Wage.
The National Living Wage for over-23s is up to £9.50 . The apprentice rate has also risen, up from £4.30 an hour to £4.81.
On Twitter, Lewis said: "Are you on minimum wage? You may be underpaid, 500,000 are! Many who think they are on minimum wage are in reality actually being paid less than they should."
MoneySavingExpert has updated its guide on the minimum wage , which includes ways to check if you are getting less than you should.
For example, if you are required to buy anything to carry out your job, like tools or a uniform, your workplace have to ensure this does not mean your wage falls below the legal requirement.
This applies however the cash is deducted. It includes you buying items in a shop, paying your boss for them or having cash taken from your salary.
If you get minimum wage, any time you spend working you should be paid for.
This includes any overtime, time spent in training, travelling time and time spent opening up or closing down a workplace.
How to check if you are underpaid
If you think you might not be getting the full minimum wage, the government has a national minimum wage and living wage calculator to help you work out what you should be getting.
You can talk to your boss informally to try to get things resolved.
Another option is to put in a formal complaint to your employer if that does not work.
You can also take the issue to Acas - the Advisory, Conciliation and Arbitration Service.
Acas is a government-backed body that steps in with workplace issues.
You can go to Acas by filling in this form or calling 0300 123 1122.
If you would rather avoid that, or you no longer work at the company, you can contact HM Revenue & Customs (HMRC) instead.
You can do so by filling in this online form.
However, you will have to tick 'yes' when asked if you're willing to be contacted by the taxman, as otherwise they may not be able to investigate.
If HMRC discovers you were not paid the proper minimum wage, it can order your employer to repay the difference, for the past six years.
It can also fine the employer and take them to court if they do not pay up.
