A seemingly simple phrase can sometimes become stubbornly opaque when the lawyers at the Supreme Court get to it, and that was the case Monday when the justices examined what “changing clothes” means .

It is part of a case brought by Clifton Sandifer and 800 current and former workers at the U.S. Steel plant in Gary, Ind. They claim federal law requires them to be compensated for the time they spend putting on protective gear before reporting to their work stations.

U.S. Steel said the workers need not be paid because of an exception in the law that allows employers and unions to agree not to pay for “any time spent in changing clothes or washing at the beginning or end of each workday.” Such an agreement is in place in Gary.

While washing is not part of the dispute, what constitutes “clothes” is at the heart of the matter.

Sandifer’s attorney, Eric Schnapper of Seattle, said that “not everything an individual wears is clothes.” He said it should not be difficult to differentiate between normal clothes and something unique that industrial workers must don and doff.

“Our test is: An item is not clothes if it is worn to protect against a workplace hazard and was designed to protect against hazards,” he told the justices.

But the U.S. Court of Appeals for the 7th Circuit didn’t accept that and previously ruled against the workers, who are required to wear flame-retardant jackets, pants, snood, gloves, wristlets and leggings.

That court took a picture of a model wearing the attire, and Justice Ruth Bader Ginsburg held it up for Schnapper. “From the picture, that looks like clothes to me,” she said.

Schnapper said this is a case in which a picture does not tell the story.

But Ginsburg said there were all kinds of jobs that require uniforms — bakers or doormen, for instance — and no one believes those workers should be paid for putting on clothing.

And there was a bit of real-life experience from the court. Chief Justice John G. Roberts Jr., who worked summers in a steel plant to help pay for college, said there were particularly thick blue jeans that workers would wear at the plant but not elsewhere. Don’t those protect from workplace hazards? he asked.

Lawyer Lawrence DiNardo, representing the steel company, said that the focus should be not on the items a worker wears but rather on the process of getting ready for work.

“Collective bargaining does not focus on whether or not a shirt is clothes or a pair of pants are clothes or protective eye gear, and that is how the statute was written,” DiNardo said. “Given those two points, the term ‘clothes’ as used in the statute was intended to encompass the work outfit industrial workers were required to change into and out of to be ready for work. “

Justice Sonia Sotomayor said that would make something like a scuba tank “clothes” for some workers. And she had other examples:

“Your definition would include somebody spending an hour of putting on a suit of armor if he’s going to be a jouster. It would include the space people who put on that complicated white suit that has all the connections to equipment.”

The government proposed that the court differentiate between clothes and equipment.

“For instance,” said Assistant Solicitor General Anthony A. Yang, “the meatpacker might have a chain mail” kind of sleeve, chain-mail gloves and a plexiglass “belly guard” as part of his work attire. Those would not be considered “clothes,” he said.

Interest groups representing manufacturers and others said a ruling in favor of the workers could have a huge impact in back pay and other costs.

At the end of the hour-long argument, Justice Elena Kagan wondered why a government agency had never tackled the question of what the statute means when it says “clothes.”

Schnapper said he did not know, but Justice Antonin Scalia offered a reason.

“Too complicated is why,” he said.

The case is Sandifer v. U.S. Steel.