HM Revenue & Customs has been accused of "bully boy tactics" for sending high earners letters asking why they are not paying more tax.
Around 1,000 missives have been issued to people who have an income of more than £150,000 but are paying less than 22% in tax.
The letters state: "We can see from your Self Assessment tax return... that your effective rate of tax is lower than the average for people in your income bracket.
"There may be reasons why your effective rate of tax is correct. But it could mean that there is something wrong with your self assessment."
Mike Down, of accountancy firm Baker Tilly, said HMRC should be checking tax returns to see whether individuals had already explained their circumstances.
He told the Daily Telegraph they had seen examples including an elderly widow whose effective tax rate was low because she was giving more than half her income to charity.
"The Revenue is adopting a computer says yes approach, rather than simply checking the tax returns," said Mr Down.
"These bully boy tactics do not help anyone, instead they just scare innocent taxpayers."
An HMRC spokeswoman said: "We are issuing 1,000 letters to taxpayers with an income of £150,000 or more who have an effective rate of tax of 22% or less.
"If a taxpayer is content that their return is accurate then they do not need to do anything.
"This is part of a trial to help individuals identify any mistakes they may have made on their Self Assessment return. Anyone who needs help is welcome to get in touch with us."