What started as a legal challenge of California’s milk pricing system by dairies in two states has grown into a legal challenge by eight states that will be heard before the U.S. Supreme Court on April 22.

Nevada-based Hillside Dairy and Ponderosa Dairy in Arizona originally filed suit in 1997 challenging the California milk pricing system because it forces out-of-state milk producers to sell milk to California processors at an artificially low price because of an in-state subsidy system. A situation that they contend interferes with the interstate commerce clause of the U.S. Constitution. A district court rejected their claim, and a federal appeals court also denied their appeal in August. In early January the U.S. Supreme Court said it would hear the case.

States filing legal briefs in support of the lawsuit include Wisconsin, Nevada, Minnesota, Montana, Oregon and Washington.

Wisconsin Secretary of Agriculture Rod Nilsestuen, says the suit is an opportunity to “level the playing field” for dairy producers across the country that compete with California’s protectionist pricing system.

California developed its own milk pricing system in the 1960s and claims that the federal Agricultural Improvement and Reform Act insulates its milk laws from the commerce clause.

Associated Press, Milwaukee Journal Sentinel