The Volokh Conspiracy discusses the Ninth Circuit’s opinion in Perry v. Schwarzenegger here.  From the opinion:

Plaintiffs served a request for production of documents on [the Proponents of Prop. 8], seeking, among other things, production of Proponents’ internal campaign communications relating to campaign strategy and advertising. Proponents objected to disclosure of the documents as barred by the First Amendment…. [T]he district court rejected Proponents’ claim of First Amendment privilege….

We reverse. The freedom to associate with others for the common advancement of political beliefs and ideas lies at the heart of the First Amendment. Where, as here, discovery would have the practical effect of discouraging the exercise of First Amendment associational rights, the party seeking discovery must demonstrate a need for the information sufficiently compelling to outweigh the impact on those rights. Plaintiffs have not on the existing record carried that burden in this case….