Noting that section 8(b) was intended to preserve "the right of labor organizations to bring pressure to bear on offending employers in primary labor disputes"
In Joliet Contractors Assn. v. Labor Board, 202 F.2d 606, cert. denied, 346 U.S. 824, the Court of Appeals for the Seventh Circuit held that a glaziers' union boycott of preglazed sashes to preserve work they had traditionally performed was an unfair labor practice under ยง 8(b)(4).