Columbia subject headings:
Open and closed shop--United States--States.
Harvard subject headings:
Labor unions--United States
Open and closed shop--Law and legislation--United States--States.
Open and closed shop--Law and legislation--United States.
Open and closed shop--United States--States.
Open and closed shop--United States.
Princeton subject headings:
Labor unions--United States.
Open and closed shop--Law and legislation--United States.
Open and closed shop--United States.