"[The] Court held that the Yard-Man line of cases, 'a thumb on the scale' in favor of construing retiree health benefits provided through collective bargaining as irrevocable lifetime promises, was 'not compatible with ordinary principles of contract law.' On that point, the Court was unanimous. A concurring opinion by four Justices suggested, however, that disagreement remains on exactly how 'ordinary principles of contract law' affect the interpretation of welfare benefit plans." [M&G Polymers USA, LLC v. Tackett, No. 13-1010 (U.S. Jan. 26, 2015)]