Four employees fired by Google right before Thanksgiving plan to file an unfair labor practices complaint this week with the National Labor Relations Board, charging that the company fired them for engaging in protected labor organizing.

Why it matters: The prospect of engineers challenging an iconic Silicon Valley firm under well-established labor laws could mark a sea change for the largely non-unionized tech industry.

Google's side: A statement to the press from Google last week referred to "an increase in information being shared outside the company" and said the four employees were let go because they were found to be "involved in systematic searches for other employees’ materials and work. This includes searching for, accessing, and distributing business information outside of the scope of their jobs."

In a new statement today, A Google spokesperson said the firings were the result of "intentional and often repeated violations of our longstanding data security policies... No one has been dismissed for raising concerns or debating the company's activities."

The workers say the suggestion that they leaked information is "flatly untrue" and that they believe they were fired for their activism in various causes within Google, including organizing against the company's potential work with Customs and Border Protection.

"The company’s code of conduct states unequivocally: 'don’t be evil, and if you see something that you think isn’t right — speak up!' And we did," the four fired Googlers wrote on Medium.

What they're saying: In an interview with Axios, the four fired employees — Laurence Berland, Paul Duke, Rebecca Rivers, and Sophie Waldman — said their firing a week ago was abrupt and left them trying to line up legal representation over a long holiday weekend.

"This feels very much about scaring people who are trying to come together to act," Duke said.

"This isn't really about us — this is about the hundreds of thousands of people who work at the company, and Google's fear of their power," Berland said.

The big picture: Google has recently faced challenges from employees on several fronts, including:

Ethical controversies that have sparked employee unrest, including a now-scuttled project named Dragonfly to re-enter China's search market with a product censored to satisfy the Chinese government, and a now-cancelled joint research project with the Pentagon called Maven aimed at using AI to analyze imagery from drones.

that have sparked employee unrest, including a now-scuttled project named Dragonfly to re-enter China's search market with a product censored to satisfy the Chinese government, and a now-cancelled joint research project with the Pentagon called Maven aimed at using AI to analyze imagery from drones. Charges of bias included complaints from some conservative employees that the company's culture suppresses their point of view — and from outside critics on the right who maintain, with little evidence, that Google search is biased against them.

included complaints from some conservative employees that the company's culture suppresses their point of view — and from outside critics on the right who maintain, with little evidence, that Google search is biased against them. A previous challenge at the NLRB over employee complaints that Google had stifled their freedom of workplace expression. In September, Google reached a settlement with the NLRB that required the firm to post public statements reminding employees of their rights.

What to watch: Other companies will closely follow how far Google's engineers go in organizing further protests, and how much leverage they are able to bring to bear.

Our thought bubble: Google's cherished freewheeling culture of debate has already taken lots of blows. Whatever happens at the NLRB, the company is likely to find it extremely difficult to turn back the clock to its startup-era heyday of free expression and management-employee trust.

Go deeper: Tech's new labor unrest

Editor's note: This story has been updated with a new statement from Google.