He added: "We were therefore surprised to be singled out in the way that occurred, not only through a retroactive change of law but the effective naming of Barclays by the exchequer secretary in his statement to parliament, accusing the bank of entering into a 'highly abusive' scheme.
The regulator said Mr. Eagle had shown "a breathtaking disregard" for his clients when he deliberately set out to pump up the share price of a computer parts company, Fundamental-E Investments, in a complex, prolonged and "abusive" scheme for his own benefit.
In theory, an abusive pyramid scheme that produces scores of failed recruits should generate a steady stream of complaints.
William A. Ackman, a hedge fund manager, has called the company an abusive pyramid scheme and said the stock was essentially worthless.
Mr. Ackman, the head of Pershing Square Capital Management, contends that Herbalife is an abusive pyramid scheme, an argument that he first outlined when he revealed his large short-selling position in December.
The company, which Mr. Ackman has accused of being an abusive pyramid scheme, sells its products through a network of independent distributors, who turn around and sell to customers or consume the products themselves.
"This agreement is about any type of abusive scheme," she said, vowing to look for those who "are trying to drop out of the system".
A description of the tax deduction technique in this shelter is being added to a Treasury Department list of abusive schemes that tax professionals are required to know about and that cannot be used in preparing future tax returns.
The lawsuit aims to end abusive schemes by which partisan operatives, exploiting the secrecy provided by the I.R.S. shield, bankroll political attack ads and other campaign agendas.
Ministers are understood to have hardened their attitude over a new so-called "generalised anti-avoidance rule" after the government took the extremely unusual retrospective action to close down the two "highly abusive schemes".
