The lawyer representing UK Uncut has told International Business Times UK that he is "ready" to take on HM Revenues & Customs in court over the Goldman Sachs affair.
Richard Stein, of Leigh Day, will formally begin legal proceedings against the tax department after he received a "dismissive letter" from HMRC about a settlement made with the merchant bank which critics say cut its tax bill by £10 million.
He said: "They stalled replying to us for nearly two months and when they did finally get back to us they said we didn't have a case, which is untrue.
"Back in the 90s, Goldman had a number of offshore accounts that waived National Insurance. But HMRC forced the bank, among 21 other companies, to pay back the NI which Goldman refused to do. When they lost their battle in court years later, HMRC made a private deal to allow the bank to pay back the capital amount but was let off the interest repayment."
The settlement, made in secret, has angered politicians, lobby groups and the public who claim there is £25 billion of outstanding tax, including Goldman's £10 million.
An HMRC spokesman said: "We collect 98 percent of tax due. The rest can't be collected due to insolvency rules. It's a myth that there is a large amount of tax waiting out there to be collected."
But Stein said: "If you or I fail to pay our taxes then we expect to pay interest. That doesn't seem to be the case for the big businesses."
Uncut's action comes in the same week that the Public Accounts Committee published a damning report over how HMRC conducted itself with big corporations and criticised the relationships as "cosy".
UK Uncut launched a number of protests against the outgoing secretary for tax Dave Hartnett who last week announced his retirement from Revenues & Customs.
Tax expert Richard Murphy told the IBTimes UK earlier this week that Hartnett had become "too relaxed" with the big corporations.