Dallas-based Jenkens & Gilchrist is refusing to bow to an unprecedented de-mand from the Internal Revenue Service (IRS) to reveal the names of clients allegedly based in illegal tax havens. The IRS has served a summons on Jenkens & Gilchrist asking its Chicago office to reveal the names of more than 600 clients that the IRS believes are illegally avoiding taxes by using vehicles organised or sold by the firm. Jenkens chairman and chief executive officer William Durbin said: "Jenkens & Gilchrist has informed the IRS that the firm is prohibited by law and its ethical responsibility to its clients from complying with the demand to disclose the names of clients who have sought our legal advice." The IRS has shrugged off client-attorney privilege, claiming that lawyers should not help their clients avoid taxes. The attack on client-attorney privilege echoes tactics pursued by the Securities and Exchange Commission (SEC), the Department of Justice and the Federal Trade Commission as US authorities try to clamp down after a series of corporate scandals. Durbin has vowed to fight the IRS in the courts. He said: "It has long been the law of this country that Americans have a right to consult with an attorney in confidence, and that only the clients themselves can waive that right. Unless and until our clients inform us that they have waived that right, we cannot comply with the IRS demand." The 'John Doe' summons needs court approval, which has been granted by the US District Court, Northern District of Illinois. The IRS is investigating 92 "promoters" of abusive tax shelters, including law firms, investment banks and accounting firms. IRS chief counsel John Williams said: "We have, and will, issue summonses to law firms, accounting firms, investment banks and others who may have been involved in the promotion of questionable transactions." In a separate case pending in Manhattan Federal District Court, businessman Henry Camferdam and three associates are suing Jenkens after paying the firm $2m (£1.2m) in fees for a tax shelter that the IRS is attempting to disallow. In a statement, Durbin said: "It remains our opinion that it is more likely than not that the transactions were proper. Our opinion relied, in part, on the position the IRS itself advocated and the Tax Court adopted in 1984… The Camferdam suit is still without merit and we will continue to advance this position in pleadings that we have and will file with the court in this arbitration."