The New York City Commission on Human Rights has scheduled hearings on how the advertising industry hires, retains and promotes minority employees...16 senior agency executives are being subpoenaed to testify at the hearings. Among them are the chief executives of agencies owned by the four largest agency companies: the Omnicom Group, the WPP Group, the Interpublic Group of Companies and the Publicis Groupe. Although the industry has been working on efforts to increase minority hiring, critics have complained that not enough is being done to diversify the staffs of agencies.