Retail warehouses don’t have to pay workers for the time they spend in security screenings to make sure they’re not stealing, the Supreme Court ruled Tuesday in a unanimous decision that reverses a lower court’s finding that workers must be paid for that time.

The ruling is a blow to wage theft claims by the poorly paid workers who fill orders for Amazon.com and similar online retailers in punishing conditions with little job security. It effectively ends 400,000 workers‘ hopes of recouping hundreds of millions of dollars in back pay from the company in 13 different class-action suits.

But an employment law expert tells ThinkProgress that workers who are bringing a host of other prominent wage theft cases in other industries have nothing to fear.

“It says absolutely nothing about whether other pay practices violate the Fair Labor Standards Act,” said Prof. Catherine Keck, who teaches employment and labor law at the University of California Irvine School of Law. “I don’t think you can read this decision as anything but a very narrow interpretation of a particular portion of the law.”

The case targeted Integrity Staffing Solutions (ISS), a temp agency that Amazon pays to staff its warehouses. The warehouses require staff to clock out prior to lining up for mandatory security screenings, which workers say take up to 25 minutes to complete because the company won’t invest in setting up enough metal detectors to turn the process into a quick, simple pause on the way out of the building.

A 1947 law called the Portal-to-Portal Act exempts employers from having to pay workers for the time they spend on activities “that take place before and after the workday proper,” the New York Times explains. Workers can’t demand wages for the time it takes to walk from their car to the time clock, for example, or for the time they spend commuting. How you read on-site security screenings in the context of that law, Keck said, is a judgment call.

“There’s truth in both points of view on this. This is not like commuting,” Keck said, and “essentially the employer’s choice about how it wants to run its business and its unwillingness to invest in a security system means it is wasting a lot of its employees’ time.” But the Portal-to-Portal Act specifically says companies don’t have to pay workers for anything they do after the end of their principal work duties.

“I think that language could be construed both to include the security screenings and to exclude them. And the court chose one plausible interpretation, which is that their principal job is to put stuff in boxes in a warehouse and [not] the searches to make sure they’re not stealing stuff,” Keck said. Solving the problem requires either a change to the law from Congress to clarify how mandatory security screenings relate to existing labor law, or a decision by Amazon to spend the money it would take to make the screenings efficient enough that they don’t trap workers on site after their shift’s end.

A series of high-profile wage theft suits against McDonald’s from last spring could prove crucial to the long-running, increasingly rowdy campaign to force the fast food industry to stop paying poverty wages and start letting workers unionize. But while those suits also pivot on allegations that a corporate giant systematically deprived its most exploited employees of money they should have been paid for time they spent on site, the nature of the allegations is so different from those in the Amazon case that worker advocates have nothing to fear from Tuesday’s ruling.

McDonald’s allegedly uses a computer system to police cash flows at its stores in real time, giving managers an incentive to monitor the ratio of cash register revenue to staff wage costs from moment to moment. Workers allege that managers respond to that information by forcing them to clock out but continue working, or clock out but not go home, or otherwise manipulate their time cards and deprive them of their due pay — something multiple former managers have confirmed.

Such timesheet abuses are “clearly illegal and there’s no argument on the other side,” Keck said. “That’s a totally different issue, it arises from a totally different part of the statute.”

This blog originally appeared in Thinkprogress.org on December 10, 2014. Reprinted with permission. http://thinkprogress.org/economy/2014/12/10/3602000/amazon-wage-theft-ruling/

About the Author: Alan Pyke is the Deputy Economic Policy Editor for ThinkProgress.org. Before coming to ThinkProgress, he was a blogger and researcher with a focus on economic policy and political advertising at Media Matters for America, American Bridge 21st Century Foundation, and PoliticalCorrection.org. He previously worked as an organizer on various political campaigns from New Hampshire to Georgia to Missouri. His writing on music and film has appeared on TinyMixTapes, IndieWire’s Press Play, and TheGrio, among other sites.