On the weekend, 12 Years a Slave won the Academy Award for Best Adapted Screenplay as well as Best Picture. There has been some controversy around the authorship of the screenplay. Apparently Steve McQueen believed at one point that he should have received a writer credit, John Ridley disagreed, and so Ridley ended up with the credit and therefore the award.
These kinds of things usually don't happen. The Writers' Guild of America has literally over 50 pages in its Collective Bargaining Agreement setting out the criteria for assigning credit and, if there's a dispute between writers, the arbitration method for settling it. So why didn't that happen here?
Believe it or not, the answer may be found in labor law.
In order to work on a theatrically-released film in the USA, writers are usually required to be members of the Writers' Guild of America. But the WGA is, at the end of the day, a union. And under the First Amendment no person can be forced to be a member of a union.
Writers, just like any other person working for a unionized company, have the right to work onsite and not join the union, so long as they pay certain mandatory contributions. For example since the WGA collective agreement gives the right to health insurance and pensions as well as certain other benefits (known colloquially as "health, pension, and benefits" payments or HPB), if a unionized company wants to hire someone who isn't a member of a union then the person is still required to pay HPB payments. (Usually these are grossed up into the worker's salary.) In the entertainment industry we say that person is paying the "financial core" payments and their status is usually abbreviated as "fi-core".
The thing is, a fi-core person is only entitled to certain defined benefits, and script arbitration isn't one of them. That matters: under administrative law if a person is a member of a union and they have a grievance they have to use the union grievance rules to pursue it. So those WGA script arbitration provisions are mandatory for WGA members, and one element of them is that the arbitration decision is final.
But a fi-core individual isn't required to follow the union's rules. That means they can sue. And that means depositions, airing dirty laundry, court judgments, and all sorts of public disclosures and documents that movie studios usually hate.
I don't know if what I've just described was the case for 12 Years a Slave, but it may be relevant that John Ridley is fi-core. During the last strike he wrote a piece for the LA Times about his decision. This matters too. If Steve McQueen believed that his work deserved a writing credit alongside Ridley's, he may not have had the chance to go to arbitration to get it; he only could do that if Ridley's contract contained a provision creating such a right. That means if he had tried to claim credit he would have had to prove it.
You might think that he could have just put his name on it - after all, as the producer he controlled the product. But that's not true either: the final cut in a movie always, ALWAYS goes to the studio (unless you're Steven Spielberg or someone with that kind of juice). And if he had put his name on the project as a writer without having proof he, the movie, and the studio would all have been exposed to a lawsuit for copyright infringement: claiming someone else's property as your own is A Bad Thing(TM) and studios tend not to let projects with that kind of uncertainty go to theaters. If that's the case, easier just to let the credit go and agree with the studio you'll never talk about it again. You can look angry at the Oscars later.
And that's a problem most writers, credited or not, would kill to have.
John Ridley's explanation of why he went fi-core: