Final answer:
At least 30 percent of employees must sign authorization cards for the NLRB to conduct a representation election.
Step-by-step explanation:
For the National Labor Relations Board (NLRB) to hold a representation election, at least 30 percent of employees must sign authorization cards.
This is the minimum threshold required to indicate that there is substantial interest in the workforce to have union representation. It's important to note, this is just for the election to be held, and it does not by itself establish a union.
Reviewing other similar questions, for example, most ordinary laws require what is often referred to as a simple majority to pass, which is option (c) 50 percent, or if explicitly needed, option (d) 50 percent + 1 vote.
Also, pertaining to political representation, in the 115th Congress of the United States, option (b) 21.2 percent of the elected officials were women.