The shelters allowed taxpayers to fabricate a minimum of $2.4 billion of deductions to reduce their taxable profits, said Cynthia J. Mattson, a senior lawyer at the I.R.S., adding that the figure is likely to be many times that.
The tax agency is sending a signal to professionals and the wealthy that it will track down tax abusers. In other cases, it is seeking the names of people who bought tax shelters sold by the accounting firms of KPMG and BDO Seidman. Like the law firm, they are fighting disclosure. Two other big accounting firms, PricewaterhouseCoopers and Ernst & Young, reached agreements with the I.R.S. last year when it sought lists of tax shelter clients.
The I.R.S. won approval yesterday from a federal judge in Chicago to issue its summons to Jenkens & Gilchrist, which is based in Dallas. The law firm took in at least $72 million in fees for its tax shelters and probably much more, according to documents filed by the Justice Department.
The I.R.S. commissioner, Mark W. Everson, said that “attorneys and accountants should be pillars of our system of voluntary compliance, not the architects of its circumvention.”