The Supreme Court of the United States held that a State may not implement an open primary system that unreasonably burdens political parties' associational rights that are guaranteed by the First Amendment to the United States Constitution.
California Democratic Party v. Jones, 120 S. Ct. 2402 (2000).
Brian P. Bronson,
The California Open Primary Act Unconstitutionally Burdens Political Parties' Associated Rights: California Democratic Party v. Jones,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol39/iss4/7