AFTRA stands for The American Federation of Television and Radio Artists and is a national labor union representing over 70,000 performers, journalists and other artists working in the entertainment and news media. Any person who has performed or intends to perform professional work in any one of AFTRA's jurisdictions is eligible for membership. So when you see an AFTRA casting- they are looking for people who are in that union. You can join by going into your nearest Local AFTRA office or join online on their website.
New members must complete an application and pay a one-time initiation fee and dues for the current dues period. The initiation fee is $1,600 and minimum dues are $63.90. After joining, a member's dues are based on his or her AFTRA earnings during the previous year. Members who earned less than $2,000 annually pay only the minimum amount of $63.90. Members are billed twice a year. It is up to you if you want to join. Make sure to check out their website to see all of their benefits. Since anyone can join, it is beneficial if you are looking to do AFTRA work.