The U.S. Supreme Court on Monday struck down California's ban on the slaughter of "downed" swine, saying the state law strayed too far into federal territory.

In a case closely watched by other states as well as the multibillion-dollar livestock industry, the court unanimously ruled that long-standing federal law pre-empted California's 2008 measure.

"The California law runs smack into the (federal) regulations," Associate Justice Elena Kagan wrote.

Kagan's 14-page decision emphasized that the Federal Meat Inspection Act covers a "broad range of activities at slaughterhouses" and that it "expressly" pre-empts the state law.

The law in question prohibits the slaughter of nonambulatory pigs, sheep, goats or cattle. These are animals that can't walk because of disease, injury or other causes. The law further requires that downed animals be euthanized.

The ruling Monday specifically cited the state provision that covers swine, but the court's ruling effectively guts the entire state law.

The Federal Meat Inspection Act specifies that a state can't impose slaughterhouse protections "in addition to or different" from the federal requirements.

The National Meat Association, which represents about 300 companies, including Harris Ranch, Hormel Foods and In-N-Out Burger, argued that the law violated this pre-emption rule.