Employees indicate their willingness to be represented by a union by signing a/an:

Employees indicate their willingness to be represented by a union by signing an authorization card. People who work and represent a union sign authorization cards to show the strength in numbers of people who back the union. A union is a group of people that have formed an organization, there are people who work for a union and collectively decide whether as a whole they agree to the work force and will abide by that or go on strike.