The government (defendant) brought suit in federal court against Montana (plaintiff), challenging the constitutionality of Montana’s practice of imposing a 1 percent gross receipts tax on contractors of public construction projects, but not on private contractors. The case was continued pending the outcome of another case, Peter Kiewit Sons’ Co. v. State Board of Equalization (1973) (Kiewit I), which addressed the identical issue in state court. In that case, a federal contractor, Kiewit, challenged the tax on constitutional grounds, alleging that it impermissibly discriminated against the United States and the construction companies with which it contracted. The Montana Supreme Court held in favor of the tax, and Kiewit filed a motion for consideration. At the direction of the Solicitor General, Kiewit withdrew its motion and filed a second suit in state court, requesting refunds of tax payments not at issue in the first suit (Kiewit II). The court dismissed the complaint on res judicata and collateral estoppel grounds. After the final disposition in Kiewit, this suit was heard by a three judge panel, which held that Kiewit was not binding and struck down the tax as unconstitutional. Montana appealed, and the United States Supreme Court granted certiorari.