There are so many people who want to be actors that it would be easy for producers to take advantage of that. So actors get together and form a union for collective bargaining to do things like set minimum pay, ensure sick leave and paid vacation, payment of travel expenses, safe work conditions (not being forced to do dangerous stunts, having adequate breaks during rehearsals) and things like that. The union can mediate disputes between members and producers like if someone feels they were unfairly let go. The union also offers things like health insurance, pension plan, and classes in the business end of the industry. The bargaining power of a union comes from the fact that their very talented and trained members will only work for projects that have have the collective bargaining agreement. And because the union demands these things for their members they raise the bar and even non-union shows offer some of the benefits - which helps non-union actors as well. Some actors are proud of that.
You can t just join the union. You need to be eligible. There are two main ways to join the union. One is through their Equity Membership Candidacy Program (EMC). By working for theatres that participate in the program as an actor you accrue a point a week. Upon getting 50 points, you are then eligible to pay your initiation fee and join the union. So, 50 weeks of non-union work as an actor in an EMC participating theatre is one way to join. You can also have the option to join if you are offered and accept an Equity principle contract. This means you, as a non-union member, have been offered a union job. As such you are immediately eligible to pay the initiation fee and join. (This is how I became eligible to join.)
Technically you don t need to be a member of the union to audition for Broadway, but it s very unrealistic for a non-AEA actor to get their first union contract on Broadway. Auditions for Broadway are run by AEA. As a union requirement, the show will hold two kinds of "required Equity calls". Equity Chorus Calls (ECC) for roles in the chorus, and Equity Principal Auditions (EPA) for principal roles. The Equity union requires that producers hold an open call for EPA roles every six months. Equity members sign up early and will get priority over non-union performers. Actors auditioning are seen in order, and sometimes given numbers. The non-union performers are only seen after ALL the Equity performers have been seen (if they re seen at all - they could be dismissed if there isn t time to see them).
So being an AEA member indicates a higher level of skill then non-members. AEA tells producers that the actor has the skill and temperament to work at a professional level and it protects the actor for exploitation by the producers.
Proud former member of AEA