Kirshenbaum v. Pennsylvania Board of Law Examiners

approving injunction against foreign breach of contract action where antitrust implications of agreements were being litigated in the U.S. | payments of contractors to pension funds were not extracted by unlawful means where trustees enforced delinquency clause involving subcon tractor contributions in master labor agreement against contractors | court has power to enjoin party from bringing compulsory counterclaim as subsequent federal action