The McCaskill-Bond Amendment to the Federal Aviation Act provides that a merger of air carriers requires the new entity to merge the seniority lists of the two carriers’ employees. Republic Airways acquired Midwest Airlines, and thereafter the Teamsters Union, which represented the flight attendants at Republic’s older carriers, refused to integrate the seniority lists for flight attendants and placed Midwest’s flight attendants at the bottom of the seniority roster. A group of Midwest flight attendants challenged the action, asserting that it violated the amendment.