Benedict Coal Corporation (Benedict) (defendant) and other coal companies entered a collective-bargaining agreement with the United Mine Workers of America (United). In that agreement, Benedict and the other companies agreed to pay their employees certain wages and to put a portion of company profits into a welfare fund for the benefit of all the companies’ employees. Benedict, however, only contributed slightly more than half of what it owed. John Lewis and other welfare-fund trustees (plaintiffs) sued Benedict for not contributing the required amount. Benedict’s defense for failing to make the full contribution was that United had also violated the agreement by organizing strikes. Benedict argued that the agreement stated it was integrated, and the agreement’s prohibitions on strikes were part of United’s consideration. The terms creating the welfare fund, however, repeatedly stated that each company’s welfare fund contribution depended on the company’s coal production. The trial and appellate courts allowed Benedict to assert United’s breach as a defense in the trustees’ lawsuit about Benedict’s welfare-fund contribution. The United States Supreme Court granted certiorari to hear the case.