Less important, largely because it is less widespread, is the demand of organized labor for the closed shop. The closed shop is one in which only union laborers are employed, while in an open shop membership in a union is not required. Obviously, organized labor prefers the former kind of shop, but often circumstances are such as to force it to permit its members to work alongside what union men call "scabs." Occasionally, employers will not hire union men under any circumstance. Thus in reality there are three kinds of shops: open, closed, and nonunion. Closely related to the question of open and closed shops is the question of open and closed unions. Some unions are closed; that is, the difficulty of gaining admission, because of the long apprenticeship required or because of the high entrance fee charged, is so great as to give its members a virtual monopoly of their trade. Others are said to be open. Almost any one can on the payment of a nominal fee become a member. Many authorities believe that here lies the solution of the problem of organized labor, since the ends of both employer and employee, they contend, would be gained by making all shops closed and all unions open.