Answer: Union shop
Explanation: In simple words, union shop refers to a security clause in which the employer agrees to hire only those employees who are part of a labor union and also if they are not, they must get in one before a specified period of time.
Such clauses are made to give strength to labor rights and also to unite the labor forces so they will be safe from any exploitation in future.
Hence we can conclude that Boyd would likely go for union shop.