The case involved a plant now owned by Springdale, Ark.-based Tyson Foods Inc.
The issue was one of two that justices settled in a pair of unanimous decisions, the first rulings under the leadership of Chief Justice John Roberts in the new fall term. Roberts did not write either one.
In a defeat for business, the court said that employers must pay wages for the donning of "integral" gear and the time it takes workers to then walk to the production area.
The court, in a ruling by Justice John Paul Stevens, upheld a decision of the 9th U.S. Circuit Court of Appeals in favor of workers at a meat processing plant in Pasco, Wash. Those workers typically put on sanitary outer garments, boots, hardhats, goggles and gloves.
In a second ruling, the justices said the 9th U.S. Circuit Court of Appeals should reconsider whether federal officials can be sued for negligence over an accident in an Arizona copper mine.
Justice Stephen Breyer, writing that opinion, said the appeals court ruled too broadly in allowing the lawsuit by two men who were seriously injured in 2000 when a nine-ton rock slab fell from the ceiling of the Mission Underground Mine.
The worker pay case was the first appeal argued this term, on Oct. 3, and the first in which Roberts was presiding on the court.
The time spent putting on protective gear was not the focus of the ruling, because the Supreme Court said in a ruling nearly 50 years ago that plant workers must be compensated for time spent putting on special clothes.
Instead, the dispute focused on the time employees spend walking from place to place. Justices had been told that workers sometimes have long waits after putting on their gear.
It was not a total defeat for business. Stevens wrote that workers could not demand payment for time spent waiting in line for equipment and safety gear, when they first arrive for work.
The decision involves a Washington state plant then owned by IBP Inc., which was acquired by Tyson, and a separate Barber Foods plant in Portland, Maine.
The cases are IBP Inc. v. Alvarez, 03-1238; Tum v. Barber Foods Inc., 04-66; and U.S. v. Olson, 04-759.