A mundane calendar tool is at the center of a new controversy over Google’s power. Some Google employees think the internal tool—a browser extension that “would automatically report staffers who create a calendar event with more than 10 rooms or 100 participants,” according to a memo obtained by Bloomberg—is a way for the company to spy on worker attempts to organize. Google insists it’s just a polite reminder not to spam coworkers with event invites.

The dispute is a sign of the level of distrust within Google after a year of walkouts and protests over everything from sexual harassment to military partnerships. But it’s also an example of how workplace technology can complicate norms and regulations created in the pre-internet era.

Worker organizing can mean a lot of things. If Google were spying on actual attempts to unionize, that would be illegal, according to the National Labor Relations Act (NLRA). The question is, what counts as spying? The NLRA defines it as the company doing something “out of the ordinary” to keep track of union activity. That was an easier test to apply when spying meant a manager lurking outside a possible union meeting. It gets harder when electronic workplace surveillance has become so common.

Employers can, and do, track everything from emails, chats, and calendars to Wi-Fi usage and tone of voice, all in the name of improving their workers’ performance. In one memorable incident reported by the Wall Street Journal, a company that tracked which songs an employee listened to and which Facebook pages she visited figured out that she was sad, called her mom, and found out that she had recently been through a breakup. (The employee told the Journal that the whole event was “a little embarrassing.”)

And if checking which Facebook pages an employee is visiting is business as usual, a calendar tool isn't necessarily “out of the ordinary”—even if it just so happens to help higher-ups figure out whether there’s unionizing going on. The calendar tool would violate the NLRA if someone could prove that Google installed it only because the company got wind of a union campaign. But doing so can be hard because surveillance systems so often have multiple uses, says Data & Society labor researcher Aiha Nguyen. They can be simultaneously used for alerting people to meetings and for keeping an eye on worker dissent.

A lesser-known, and even more interesting, part of the NLRA is that it’s illegal even to give workers the impression that an employer is spying on union activity. In one case from last year, a manager at a Napleton Cadillac car dealership mentioned to another employee that he knew which of the workers was the union organizer. Since the employees had never talked to management about unionizing, the obvious conclusion was that he’d been spying on them. The National Labor Relations Board (NLRB) ended up ruling that the dealership had violated this part of labor law, among others.