No. 75-1132. Submitted October 17, 1975. Decided December 31, 1975. Rehearing and Rehearing En Banc Denied February 18, 1976. J. Dennis O'Brien, LeFevere, Lefler, Hamilton Pearson, Minneapolis, Minn., for petitioner. Marjorie S. Gofreed, Atty., N.L.R.B., Washington, D.C., for respondent. John C. Miller, Acting General Counsel, John S. Irving, Deputy General Counsel, Elliott Moore, Deputy Associate General Counsel, and Allison W. Brown, Jr., Atty., N.L.R.B., Washington, D.C., appeared on the brief