Union contracts (CBAs) usually contain one of three major types of union security clauses; 1) _______ - a person must be a current union member to be hired, 2) ______ - a new employee must join the union and pay dues within a period of time after being hired, 3 ) ------- - an employee must pay dues or equivalent fees , but is not required to join the union. Group of answer choices maintenance of membershpi / closed shop / union shop union shop / maintenance of membership / closed shop closed shop / union shop / maintenance of membership (open shop) Preferential shop / union shop / closed shop