International Salt Company (International Salt) (defendant) sold industrial-grade salt. International Salt also leased patented machinery for industrial salt processing. The machine leases forced the lessees to purchase unpatented salt tablets for the machines from International Salt. Some of the leases contained a provision that required International Salt to either match the lowest market price or else allow the lessee to buy the salt tablets elsewhere. The United States (plaintiff) sued International Salt, alleging the lease agreements were unlawful tying arrangements in violation of § 1 of the Sherman Act and § 3 of the Clayton Act. International Salt argued the leases did not create a monopoly, because some lessees could buy in the open market if International Salt did not match market prices. International Salt also argued the salt-buying restriction was necessary to ensure only high-quality salt was being used in the leased machines. The district court entered summary judgment in favor of the United States. International Salt appealed directly to the United States Supreme Court.