In a unanimous decision, the Supreme Court ruled that only the U.S. Tax Court may review refusals by the Internal Revenue Service to reduce interest payments on people who underpay their taxes.

The decision was required in the case of a couple -- John and Pamela Hinck -- assessed additional taxes. The Hincks sued for an $18,000 interest refund in the U.S. Court of Federal Claims, alleging delays in processing their case.

Chief Justice John Roberts said federal law specifies that the tax court provides the exclusive jurisdiction for such cases. The claims court said it did not have jurisdiction to consider the Hincks' suit, and the U.S. Court of Appeals for the Federal Circuit said only the U.S. Tax court had jurisdiction.

At issue is a 1996 provision in the tax code that allows the IRS to reduce interest attributable to any unreasonable error or delay by the agency.