although a minimum of 30 percent of the potential union members must sign the authorization card prior to an election unions are seldom interested in bringing to vote situations in which they merely meet the NIRB minimum. after all to become the certified bargaining unit the union must be accepted by a majority of those eligible voting workers. acceptance in this case is determined by secret ballot. this election held by the NLRB is called a representation certification and can occur only once in twelve months. thus the more signatures on the authorization cards the greater the chances the union will win certification to represent the workers.