In 2010 HMRC launched the Tax Health Plan which gave doctors and dentists three months to come forward with any unpaid tax.
Over 1,500 people came forward, including one doctor who owed £1 million, HMRC said.
Despite the plan, HMRC believes there are still around 2,500 professionals with unpaid tax bills.
The HMRC will make it clear in the letters being sent out that it holds information regarding the recipients’ affairs.
The recipient is required to respond to the letter within 21 days or face further action. For the majority that would mean a calculation of tax that is due, but in some cases it may mean a criminal investigation, with a view to prosecution, HMRC said.
The letters vary to fit the doctor or dentist's circumstances, but all deliver the same message; that they need to contact HMRC and non response is treated as an active choice.
Gary Ashford, who represents the Chartered Institute of Taxation on HMRC’s compliance reform forum, said: ‘People should not underestimate the amount of data that HMRC is holding.
‘It has been talking to medical insurance companies, pharmaceutical companies and locum agencies. What we are now seeing is HMRC starting to use that information, to identify who has not notified HMRC of all their tax liabilities.’