No. 87-1816. Argued October 28, 1988. Decided December 6, 1988. R. Henry Moore, Pittsburgh, Pa., for petitioner. Mark S. Flynn, Atty., Dept. of Labor, with whom George R. Salem, Solicitor, Allen H. Feldman, Associate Solicitor, and Charles I. Hadden, Deputy Associate Solicitor, Dept. of Labor, Washington, D.C., were on the brief for respondents. Mary Lu Jordan, Washington, D.C., and Thomas M. Myers were on the brief for intervenor. Michael H. Holland, Washington, D.C., also entered an appearance