In the memo, Google said the fired employees had repeatedly searched for, looked through and distributed information “outside the scope of their jobs.” One of the workers set up notifications to receive emails detailing the work and whereabouts of other employees without their knowledge or consent, the memo said.

“This is not how Google’s open culture works or was ever intended to work,” the memo said.

When asked last week by The Times, Google could not point to a specific rule that forbade setting up these notifications but said it was investigating to determine if this and other behavior violated the company’s code of conduct.

The Tech Workers Coalition, an advocacy group, said on Twitter on Monday that the four employees had been fired for “organizing at work” and encouraged workers at Google to “speak out against this draconian act.”

“This is meant to scare workers, don’t let it,” the tweet said.

Veena Dubal, an associate professor at the University of California’s Hastings College of the Law, said, “It does seem like this termination was in direct response to their organizing.”

She added, “I am skeptical that this was about how safe other people felt, and more about how effective these people were in the workplace in terms of organizing their co-workers.”

In August, nearly 1,500 Google workers signed a petition asking the company not to pursue a contract with Customs and Border Protection, which they said was complicit in “human rights abuses.” In September, Google hired a former member of the Department of Homeland Security staff, Miles Taylor, a move that provoked a backlash from workers who objected to the Trump administration’s family separation policy. Google deleted questions about Mr. Taylor’s employment from internal systems, BuzzFeed News reported.