The legal landscape around tracking employees is murky. There’s no federal privacy law to keep businesses from tracking their employees with GPS, and only a handful of states impose restrictions on it. In some, like Texas, Virginia, Minnesota, and Tennessee, tracking vehicles without the owner’s consent is explicitly illegal; in California, a section of the penal code forbids tracking any “movable thing,” a provision that’s been used to challenge employer tracking in the past.

But elsewhere, an employee who objects to being tracked has to fall back on asserting his or her basic right to privacy. That employee’s chances in court will depend on factors like whether or not they gave consent to be tracked, and whether the device being followed belongs to them or to the company. “It’s very vague,” said Lew Maltby, the president of the National Workrights Institute. “It’s essentially whatever shocks the judge.”

It’s hard to know just how widespread GPS tracking is in the United States, especially because companies don’t always have to notify their employees if and when they’re tracking them. A survey released last month offered a few hints: Nearly a third of people who responded said their employer tracks them by GPS, and 15 percent said they were tracked 24 hours a day. More than 22 percent said they weren’t told they would be tracked when they started their job.

The survey was paid for by TSheets, a time-tracking software company. Its apps, when installed on employees’ phones, allow businesses to track their workers on the job. The apps report each worker’s location to supervisors every five to 10 minutes. TSheets used its survey to argue that employees warm up to GPS tracking once they’re subjected to it.

A spokesperson for TSheets said the app’s location-tracking feature automatically shuts off when employees clock out for the day, but that if the employee forgets to clock out, the app will continue sending the phone’s location.

Employees can also choose to manually shut off location reporting on their phone, but what happens if they do is up to their bosses. In 2015, a woman named Myrna Arias sued her former employer, Intermex Wire Transfers, claiming she’d been fired for disabling a GPS app on her company-issued phone after she figured out that her location was being tracked around the clock. Her boss told her that the tracking app, Xora, could even tell him how fast she was driving at any point in time, according to the complaint. The case was settled out of court.

Gail Glick, the attorney who represented Arias in court, wouldn’t comment on how the case ended. But she did say that her argument, which relied in part on the section of the California penal code that restricts how GPS tracking can be used, may not have worked anywhere else. “If you’re in California, you’re kind of in la-la land,” Glick said. “We’re kind of in a bubble.”