Section 685 of the California Insurance Code imposed a retaliatory tax on out-of-state insurers doing business in California, when those insurers’ home states imposed higher taxes on California insurers doing business in those states than California would otherwise impose if business was done in California. Western & Southern Life Insurance Co. (plaintiff) was an out-of-state insurance company doing business in California. Western & Southern was taxed pursuant to the California state statute and brought suit in superior court against the State Board of Equalization of California (SBEC) (defendant). Western & Southern sought to enjoin enforcement of the tax statute on the grounds that it unconstitutionally burdened interstate commerce. The superior court ruled the tax unconstitutional, but the court of appeal reversed. Western & Southern appealed to the United States Supreme Court.