Businessmen like Lord Edmiston and Peter Cruddas have accused HM Revenue and Customs (HMRC) of a “political attack” after being sent letters demanding up to £2million.
It comes after authorities ruled payments from individuals to referendum campaigns should be treated as gifts, and therefore made taxable.
It is claimed the crackdown clobber the entrepreneurs who backed Leave the hardest, because Remain was largely funded by publicly listed companies which are exempt from the payments.
Accusations of bias have been firmly rejected by HMRC.
But Tory MP Jacob Rees-Mogg claimed the Government was “penalising people who had the audacity to challenge it” over Brexit.
He is now demanding Chancellor Philip Hammond changes the tax laws.
Mr Rees-Mogg told the Telegraph: “It is fundamentally hostile to democracy and the law should be changed urgently by amendment to the Finance Bill which is currently going through Parliament.”
And ex-chief executive of Vote Leave, Matthew Elliott, raged: “It is outrageous that HMRC are targeting EU referendum donors in this way.
“This is the Establishment having their revenge on good people who support democratic activity.
“The Treasury should intervene immediately and force HMRC to rescind the demands.”
Mr Banks, who has been asked to pay £2million on his £8.1million donation branded the demand the “revenge of the Establishment”.
Lord Emiston, who gave a total of £1million to the Vote Leave and Grassroots Out campaigns is now facing a bill of £200,000.
He told the paper: “I just feel it is against democracy.
“If any time in the future there is an issue and someone is asked ‘would you mind supporting this particular position’, the Revenue are going to jump on your back.”
Banker Mr Cruddas plans to challenge his demand after facing a demand for £180,000 after £900,000 donation to Vote Leave.
He has branded the sum “completely outrageous”.
An HMRC spokesman said: “Donations to campaign groups don’t qualify as exempt gifts to political parties, unless the recipient is a political party meeting the criteria set out in section 24 of the Inheritance Tax Act 1984.”
“No special exemption was granted ahead of the 2016 referendum.
“The legislation is applied without regard to the policies of organisations, groups or parties.”