The Chartered Institute of Taxation has urged taxpayers to check the amount of tax being deducted by employers and pension companies through the Pay As You Earn system.
HM Revenue & Customs introduced a new computer system this year and the Chartered Institute of Taxation say "huge numbers of people" may have received the wrong tax code information.
Chartered Institute of Taxation president Andrew Hubbard said:
"Most people on Pay As You Earn are used to assuming that what the taxman sends them is correct. Many file away coding notices without even bothering to check them.
"But this year, many of them are being given wrong information and unless they spot it and tell HM Revenue & Customs, their employer will receive the wrong information too and they could get a nasty shock when they open their April pay packet and see it is as much as a hundred pounds lighter than they are expecting.
"The Government should launch an urgent publicity campaign to highlight what has happened and tell people what they can do about it.
"They also need to add a specific warning about it to the majority of P2 notices - the letters containing tax code information - which have still to go out.
"This comes at the worst possible time of the year for HM Revenue & Customs, whose enquiry systems are already stretched to capacity by people seeking advice ahead of the self-assessment deadline at the end of January.
"The new Pay As You Earn system is potentially very good and this is really just a teething problem - but a serious one that HM Revenue & Customs need to warn taxpayers and their advisers about and help them resolve."
** Additional Tax Information & advice **
Depending on your circumstances, however, you may want to speak with a tax solicitor. You can find a solicitor for free via solicitor matching services, which can also help you to understand the best course of action for your situation and whether you are ready to hire a solicitor.