No. 20838. July 15, 1971. Charles Kelso, Atlanta, Ga., for petitioners; Stewart T. Graham, Fisher Phillips, Atlanta; Ga., on brief for Rust Engineering Co., John O. Gibson, Fowler Gibson, Loudon, Tenn., on brief for Sheet Metal Workers. Howard C. Hay, N.L.R.B., Washington, D.C., for respondent; Arnold Ordman, Gen. Counsel, Dominick L. Manoli, Associate Gen. Counsel, Marcel Mallet-Prevost, Asst. Gen. Counsel, Nancy M. Sherman, Stanley J. Brown, Attys., N.L.R.B., Washington, D.C., on brief. Before