No. 77-2214. Argued July 11, 1979. Decided July 2, 1980. Vivian A. Miller, N.L.R.B., Washington, D.C. (John S. Irving, Gen. Counsel, John E. Higgins, Jr., Deputy Gen. Counsel, Carl L. Taylor, Associate Gen. Counsel, Elliott Moore, Deputy Associate Gen. Counsel, Washington, D.C., on brief), for petitioner. Robert E. Paul, Arlington, Va. (Spelman, Eisenberg, Paul Wagner, Arlington, Va., on brief), for intervenor. N. Peter Lareau, Baltimore, Md. (Venable, Baetjer Howard, Baltimore, Md., on brief), for