On August 1, four California voters filed a federal lawsuit against the new California law on presidential candidate tax returns and ballot access. Griffin v Padilla, e.d., 2:19cv-1477. The case is assigned to U.S. District Court Judge John A. Mendez, a Bush Jr. appointee. See here for the complaint.
One of the plaintiffs is a registered Democrat. The Complaint points out that four Democratic presidential candidates have not revealed their federal income tax returns. They are Joe Biden, Julian Castro, Tulsi Gabbard, and Andrew Yang. This lawsuit is being handled by Judicial Watch, a conservative organization based in Washington, D.C.