WASHINGTON — Nearly 80 years ago, Congress set a few simple rules for how workers should get paid. Employers and their employees have been warring over them ever since.

The latest battle, which goes before the U.S. Supreme Court on Wednesday, was launched by former warehouse workers for Amazon.com, who argue they should have been paid for the time they spent waiting in security lines after their shifts. The case could have massive implications – not just for one of the world’s largest retailers but for employees everywhere – in further defining how companies across the country should pay for a day’s work.

The warehouse workers’ case has also helped highlight the strangely hazy precedent governing when American workers have a right to make money. Walking from your car to the workplace? No pay. Waiting for clearance before going into work at an airport or nuclear-power plant? No pay. Putting on protective gear before you start work in, say, a meatpacking plant? Pay.

“These issues have been percolating for 80 years,” said Paul Secunda, a law professor and director of the labor and employment law program at Marquette University Law School. “Think about every day for 25 minutes, thousands of employees going through a security line. Think about what they make an hour. … Now we’re talking about thousands of employers, with even larger workforces, who pay even more money. We’re talking about billions and billions of dollars. This is a very big deal.”

The Amazon case was filed by former workers at its sprawling fulfillment centers in Nevada, whose jobs included grabbing items from shelves and packaging them for delivery. After clocking out at the end of their shifts, they were expected to empty their pockets and walk through metal detectors to prove they weren’t stealing from the warehouse.

Those security lines could take more than half an hour, the workers said, and that was time when they should have been getting paid. Since 2010, more than 400,000 workers have filed a dozen class-action suits arguing they’re owed hundreds of millions of dollars in damages.

Their case, they argued, was clear-cut: The company required employees to pass through the screenings – meant to catch “shrinkage,” the industry term for workplace theft – making it an unavoidable part of their work.

Employees also complained that the contractor could have easily sped up the waits by opening up more security lines, but they had little incentive to do so, because they weren’t paying for workers’ time.

But Integrity Solutions Staffing, a staffing agency for Amazon, has argued in court briefs that the lines are just like any other workday annoyance that employees don’t get paid for: waiting to punch in the time clock, walking into work from the parking lot, or waiting to pick up a paycheck.

Integrity attorney Paul Clement has argued that “in the post-9/11 world, security screenings have become ubiquitous in the American workplace” and are a routine requirement for employees. A ruling for the Nevada workers, he said, would open “employers up to billions of dollars in retroactive damages.”

If the Supreme Court sides with the workers, the case – Integrity Staffing Solutions, Inc. v. Busk – would move forward in federal court.

Amazon said it would not comment due to the pending litigation, but a spokesperson said the “data shows that employees walk through post shift security screening with little or no wait.” (Amazon.com chief executive Jeffrey P. Bezos owns The Washington Post.)