California law prohibits employers that receive state money from interfering with union organizing. The United States Supreme Court heard arguments yesterday in a case challenging the California law, Chamber of Commerce v. Brown, no. 06-939. The employers who initiated the suit claim that the National Labor Relations Act preempts the state regulations, but the Ninth Circuit disagreed and upheld the legislation.
How the Supreme Court decides this case will have major implications for labor agreements included in CBAs, since it directly questions the power of state and local governments to regulate private labor relations matters.
For more information on the case, see the ScotusWiki entry and the analysis of the oral arguments from the Workplace Prof Blog.