On May 25, 2011, the U.S. Court of Appeals for the Federal Circuit revamped the inequitable conduct doctrine, under which courts refuse to enforce otherwise valid patents based on findings that the patent owner engaged in inappropriate conduct during the patent application process. In an effort to reduce the frequency with which inequitable conduct claims are raised by defendants in patent infringement cases, the en banc court, by a 6-5 vote, adopted significantly more stringent rules for establishing such claims. The decision was a victory for WLF, which filed briefs in the case urging the adoption of more stringent rules. WLF argued that the inequitable conduct doctrine has been invoked far too frequently to strike down patents based on relatively trivial errors. The court agreed with WLF that a patent should not be invalidated unless the patentee’s misstatement or omission before the Patent and Trademark Office was the “but-for” cause of the patent being issued.