Sundar Pichai, chief executive officer of Google Inc., speaks during the Google I/O Developers Conference in Mountain View, California, U.S., on Tuesday, May 8, 2018.

Google leadership may consider the leaking of sensitive information by employees as the biggest threat to its culture. But the more pressing issue the company faces is a massive wave of activism that's now turned some of its loudest critics into heroes.

After weeks of investigation, Google fired four employees on Monday, claiming they shared confidential documents and breached security. In an internal memo, the company's security and investigations team called it a "rare" case.

News of the dismissals went viral immediately because all four employees had either organized or participated in petitions or protests against the company. At least two of them identified as LGBTQ. The group earned the label the "Thanksgiving Four" because of the timing of the firing ahead of the holiday, and employees past and present weighed in on social media with their own stories of being targeted by leadership for their activism.

Just hours after the firings were reported, Google organizers posted a blog entry titled, "Google's Next Moonshot: Union Busting." The post, which didn't include the names of any authors, claimed that Google framed the employees.

"They think this will crush our efforts, but it won't," the post said.

U.S. Sens. Bernie Sanders and Elizabeth Warren, two of the leading Democratic candidates for president, chimed in Tuesday evening on Twitter with their support for the employees and criticized Google for being "anti-worker."

While Google parent Alphabet continues to crank along financially, pushing the stock up 26% this year, the company appears to be limping toward the 2019 finish line as tempers rage between top brass and rank-and-file staffers. Google recently ended a tradition of weekly all-hands meetings after 20 employees in San Francisco protested the treatment of two employees, Laurence Berland and Rebecca Rivers, who had been placed on sudden and indefinite administrative leave for allegedly sharing sensitive information.

The latest flare-up follows a settlement between Google and the U.S. National Labor Relations Board in September, which called on the company to allow greater debate and more open discussion on campus after an employee filed a complaint last year, alleging Google restricted free speech and fired him for expressing conservative views.

Far from establishing a truce, the agreement with the NLRB has created even more tensions, with The New York Times reporting last week that Google hired a firm known for its anti-union efforts to help it deal with rising unrest.