In Carpenters Local 60, v. NLRB, 365 U.S. 651, 81 S.Ct. 875, 6 L.Ed.2d 1 (1961) the Supreme Court indicated that where there has been no actual compulsion to join a union, even though there has been an unfair labor practice in the maintenance of an unlawful closed shop preferential hiring agreement, the imposition of the Brown-Olds remedy is punitive, and beyond the power of the Board.