United States antitrust law
Although the patents had expired by the early 1980s, Pilkington had licensed their use, and required the licensees to keep the details of the float glass process secret. Guardian Industries had tried to challenge Pilkington's dominance but had made a secret agreement to prevent new entrants into the market, with Guardian taking the lead to enable Pilkington, a British company, to reduce its exposure to United States antitrust law.