ASHINGTON, March 7 - The Supreme Court rebuked the United States Tax Court on Monday for its adoption of a "bold" and unauthorized procedure that shields essential documents from disclosure to people with cases before the court and to federal judges who review the tax court's work on appeal.

A strongly worded 7-to-2 decision, with the majority opinion written by Justice Ruth Bader Ginsburg, was addressed to the tax court's use of "special trial judges," auxiliary judges who conduct trials and make recommendations to the 19 regular judges on how major tax cases should be decided.

Under the tax court's rules, while the recommendations of the special judges are not binding, their findings "shall be presumed to be correct," and the regular judges are expected to defer to them. The reports are therefore extremely important to the tax court's decision-making process, yet since 1983 the court has regarded them as confidential internal documents and has refused to make them available to the parties or to appellate judges.

Neither federal law nor the tax court's rules authorize such "concealment," Justice Ginsburg said, adding, "In comparison to the nearly universal practice of transparency in forums in which one official conducts the trial (and thus sees and hears the witnesses), and another official subsequently renders the final decision, the tax court's practice is anomalous."

The decision was a posthumous victory for a prominent tax lawyer, Burton W. Kanter, who along with two other men was found liable for a $30 million tax deficiency in a case that dated to the 1970's. Although the decision did not overturn the tax court's 1999 judgment against Mr. Kanter and the two others, the court will now have to disclose the basis for its adverse finding and will have to change its procedures for future cases. Mr. Kanter died in 2001.

The case has been carried on by his estate and by Claude M. Ballard, whom the Internal Revenue Service accused of cooperating with Mr. Kanter in a fraudulent scheme to avoid tax liability. The case is Ballard v. Commissioner, No. 03-184.

Under the tax court's procedure, the case was heard in a five-week trial in 1994 by a special trial judge, D. Irvin Couvillion, who spent four years writing his report and recommendation. A regular tax court judge, Howard A. Dawson Jr., then issued the formal judgment, a 600-page document that bore the label "opinion of the special trial judge" and that imposed substantial penalties for tax fraud.

But one of the taxpayers' lawyers received information suggesting that Judge Couvillion had actually reached the opposite conclusion, and that the formal judgment did not reflect his findings. The taxpayers filed three motions seeking access to the original report and were refused each time, with the tax court maintaining that the report was part of the "internal deliberative processes of the court" and could not be disclosed.

In her opinion on Monday, Justice Ginsburg said that whatever the validity of the tax court's rules, they did not provide for a "joint enterprise" in which the regular tax court judge "treats the special trial judge's report essentially as an in-house draft to be worked over collaboratively."

Noting that the court's rules require the regular judges to give "due regard" to the special judge's findings, she said, "One would be hard put to explain, however, how a final decision maker, here the tax court judge, would give 'due regard' to, and 'presume to be correct,' an opinion the judge himself collaborated in producing."

Justice Ginsburg strongly suggested that if the tax court did provide for the joint procedure in its rules, the rules would then be subject to further challenge.

While assailing the tax court, the opinion was also notably critical of the executive branch for defending the procedure. "It is curious that the commissioner, always a party in tax court proceedings, argues strenuously in support of concealment," it said.

Chief Justice William H. Rehnquist filed a dissenting opinion, joined by Justice Clarence Thomas. "The tax court's compliance with its own rules is a matter on which we should defer to the interpretation of that court," Mr. Rehnquist said.

The National Federation of Independent Businesses praised the decision. "Taxpayers fighting an unfair tax bill should have the tools and information needed to mount a fair fight," Karen Harned, of the business group's legal foundation, said in a statement.

Richard H. Pildes, a professor at New York University Law School who represented the Kanter estate, said the decision addressed "very, very fundamental issues about the basic structure of a trial."

The case was unusual in that every federal appeals court to address the issue had upheld the tax court. The Supreme Court usually agrees to hear only cases that have produced lower-court conflicts. The decision Monday overturned rulings of two federal appeals courts, the Seventh Circuit in Chicago and the 11th Circuit in Atlanta.