Los Angeles is famously the home of the American film and television industry, and the various tradespeople who work for the industry are represented by a number of unions. Many of these unions also have branches in New York City, where certain television shows and all the national news broadcasts are produced. The unions are of interest to casual fans due to their role in strikes.
The above-the-line unions (starring cast, writers, producers and directors) include the Writers Guild of America, the Screen Actors Guild, the Directors Guild of America, and AFTRA (the American Federation of Television and Radio Artists). There are many below-the-line unions too (the rest of the crew and non-starring cast), the most notable of which are the Teamsters and IATSE (the International Alliance of Theatrical Stage Employees).
The unions handle their members' credits, healthcare, and pensions; and bargain individually with the AMPTP (Alliance of Motion Picture and Television Producers), the collective face of the various entertainment conglomerates (which seems like media collusion, but isn't for some reason).
The unions receive residuals from the studios. "Residuals" are the unions' share of the royalties that the publisher of a film or series earn. Residuals are important to the 'middle class' of above-the-line unions, as they help keep one solvent during the inevitable career downturns. The unions can best be categorized by their relationship with residuals and their bargaining positions with the AMPTP.
Above The Line
Writer's Guild of America (WGA)Composed of about 10,000 members, the WGA is actually made up of two groups, WGA East and WGA West, which handle their respective sides of the Mississippi River (which is really to say "New York City" and "Los Angeles"). The two sides used to have beef, but they kissed and made up in preparation for the 2007 strike. The WGA are well organized for a union of creative types, and are aggressive in their negotiations with the AMPTP. As unions go, they're pretty well-rounded.
Residuals are important to WGA members, who earn an average of $65,000 per year, not much by LA standards (even less by New York standards). Additionally, only about half of the membership make ANY money in a given year. Most of the WGA members are TV writers, so their needs tend to steer the direction of the union.
Director's Guild of America (DGA)The DGA reps directors in addition to a variety of below-the-line types (unit production managers, assistant directors, etc). The DGA considers themselves the "gold standard" of unions and they remain aloof from the others. They maintain a clubby relationship with the AMPTP (some would say too clubby) and have only gone on strike once (a symbolic affair that lasted a few hours). Most of the DGA couldn't care less about residuals: the majority are below the line (who don't get residuals), and most of the actual directors make so much money up front that they don't rely on residuals at all. As a result, the DGA demands tend to center around first class airline tickets and possessorial credit ("a film by..."). The selection of DGA leadership is a mysterious process. Currently Michael Apted serves as president, but National Director Jay Roth has the power.
Screen Actor's Guild (SAG)The largest of the above-the-line unions, with more than 100,000 members. Ronald Reagan once served as its president for five years. The vast majority of these members are struggling actors, the kind who appear as extras or waiters. The average SAG member makes about $7,000 a year from acting, meaning that they have a lot of "down time" (i.e. working-menial-jobs-trying-to-make-ends-meet time). As the bulk of SAG's membership is chronically unemployed, they have little to lose from a strike, which gives SAG a reputation for 'craziness'.
SAG also reps movie stars, but the A-listers are too rich to care about residuals, and most have sweetheart producing deals with the studios. The stars that do support strikes do so less out of financial self interest and more out of a personal liberalism. The sheer numbers-advantage that the sporadically-employed have in the union have caused many to suggest stripping voting rights from all but a select few; unsurprisingly, that measure has been unpopular.
SAG is quite well known for their controversial "Global Rule One", which bars their members from working in non-union environments. This made it especially difficult for voice actors who had entered the voice acting business through anime (like Steve Blum and Crispin Freeman) to reprise some of their old roles, as most anime dubbing projects are considered non-union note . Needless to say, the Global Rule One is one of the main reasons that there is limited work for their members and some of them even had to work in non-union shops under a pseudonym to work around this rule.
There is an out, however. Under current US labor law (not just Hollywood unions) an individual can claim "financial core" status (which is why some union voice actors, such as Stephanie Sheh, Wendee Lee, Liam O'Brien, and Matthew Mercer are able to work on non-union dubs, in addition to doing union-only work). This requires the individual to pay union dues, and allows them full union protection on union jobs, but does not obligate them to honor the union's bylaws (such as the aforementioned "Global Rule One"). Mentioning this to a SAG diehard however is a bad idea, and they've routinely put out notices about how "fi-core" will eventually be the end of organized labor as we know it.
Another phrase you may hear bandied about is someone being "Taft-Hartleyed". This refers to a provision in the Taft-Hartley Act which allows a non-union worker with an "essential quality or skill" to be hired for a union job if no union member with that skill can be found. In practice, this gives a non-union actor a one-time Get Out Of Dues Free card to work on a union production for up to 30 days (assuming they fill out the correct paperwork); at the end of that period, they have to either join SAG-AFTRA, or cease working on union productions until they do.
American Federation of Television and Radio Artists (AFTRA)The Jan Brady to SAG's Marsha. Initially, AFTRA handled videotaped production (along with radio news anchors, commercial announcers, jingle singers, some videogame voiceover artists, and the rare Radio Drama player since the end of the Golden Age of Radio) while SAG handled film, but modern technology has eliminated that distinction. SAG and AFTRA have a complex history: at one point SAG considered buying AFTRA, but they opted not to. Then in 2011, the two unions merged, becoming SAG-AFTRA.
AFTRA has better relations with the AMPTP, as they have more to gain by expanding their jurisdiction. The AMPTP said in 2009 that they would make their shows AFTRA had SAG opted to strike.
Policy and membership requirements wise, AFTRA was less strict than SAG, and both AFTRA and SAG had conflicted with each other in the past on these issues.
Producers Guild of America (PGA)The real union for Producers (Take That! AMPTP!). Arguably the least active union in Los Angeles.
Below The Line GuildsThe Below The Line Guilds represent the various members of film crews. Generally, they resent strikes, as it puts them out of work and they see little gain (you could try pointing out that a key figure regarding the AMPTP's contribution to their health care plan hinges on WGA residuals, but believe me, they do not care). A small minority of below the line union members sympathize with the above the line unions, bonded by a shared hatred of management and a belief in the power of organized labor.
International Alliance of Theatrical Stage Employees (IATSE)A large and powerful union whose favored tactic is early negotiations with the studios. Their president, Thomas Short, was a vocal opponent of the Writer's Strike. He remains a controversial figure in the world of organized labor.
IATSE and the WGA have a longstanding jurisdictional beef over animation writers. The WGA claims that writing is writing (The Simpsons, Family Guy and American Dad! are all WGA shows); IATSE claims that they belong in the cartoonists' union. This remains a hotly-debated issue, and can provoke real life flame wars.