Five other states are joining Missouri's fight against a California egg law that would prohibit the sale of eggs produced by hens kept in cages that don't meet California's size and space requirements.
Missouri Attorney General Chris Koster filed a lawsuit last month against the measure set to take effect next year.
The five other states joining are Nebraska, Alabama, Oklahoma, Kentucky and Iowa. Those states and Missouri produce 20 billion eggs per year, and 10 percent of that production is sold in California.
The state attorneys general contend the California law violates the interstate commerce clause of the U.S. Constitution by effectively imposing new requirements on out-of-state farmers.
The Humane Society of the United States has criticized the lawsuit, saying it wastes taxpayer dollars.