Google has fired four employees in what activists within the company describe as an attempt to "crush" workers' attempts to organise.
The people, who have been dubbed the "Thanksgiving Four", had their contracts terminated on Monday.
Staff were told via an internal memo that the firings were related to data security and employee safety.
But those who lost their jobs have said they were being punished for "speaking out".
The sackings followed a demonstration at Google's San Francisco office on Friday, attended by more than 200 Google employees. Two of the four fired employees, Rebecca Rivers and Laurence Berland, spoke at the protest.
The Silicon Valley giant has confirmed the authenticity of the memo, first published by Bloomberg, but would not comment further.
Google's Security and Investigations team said the employees were routinely accessing information about other projects and employees inappropriately.
"Our thorough investigation found the individuals were involved in systematic searches for other employees’ materials and work,” the memo read.
"This includes searching for, accessing, and distributing business information outside the scope of their jobs - repeating this conduct even after they were met with and reminded about our data security policies.
"This information, along with details of internal emails and inaccurate descriptions about Googlers’ work, was subsequently shared externally."
At Friday's protest, Ms Rivers told the crowd she had been put on administrative leave for accessing confidential documents. She tweeted on Monday that her contract had been terminated.
"Four of our colleagues took a stand and organised for a better workplace," a statement representing the Four, and other organising employees, read. The confirmed Mr Berland was among the four. The other two employees’ identities have not been made public.
The statement continued: "This is explicitly condoned in Google's Code of Conduct, which ends: 'And remember… don’t be evil, and if you see something that you think isn’t right – speak up’.
"When they did, Google retaliated against them. Today, after putting two of them on sudden and unexplained leave, the company fired all four in an attempt to crush worker organising.”
Among the issues causing discomfort among Google employees is the firm's work with the US Border Patrol. More than 1,500 workers have signed a petition demanding Google backs down from its bid to provide the agency with cloud computing services.
But the workers point to Google's hiring of IRI Consultants, a firm which bills itself as a leader in helping major firms avoid "union vulnerability”, as a sign of the search giant’s growing unease at internal activism.
The row has caught the attention of Washington. "This type of union busting is unacceptable," tweeted presidential hopeful Senator Bernie Sanders.
"I say to Google: it is time to address the racism, harassment, and harmful contracts at your company and treat your workers with the respect and dignity they deserve."
End of an open era
Observers see the move as heralding the end of Google's famously open working culture. Executives have locked down the degree to which employees can access information on projects they are not involved with, while earlier this month Google's chief executive Sundar Pichai told staff its weekly "all-hands" meeting would no longer take place.
The open forum, which used to take place every Friday, will be replaced by a monthly meeting that focused only on "product and business strategy", according to tech news site The Verge, referencing an internal memo sent at the time.
No longer allowed at the meetings: free-flowing questions on Google's political controversy, such as its role in China, dealings with the military, and co-operation with US Immigrations, Customs and Enforcement - known as Ice.
"They think this will crush our efforts, but it won't," the Google workers statement distributed on Monday added.
"For every one they retaliate against, there are hundreds of us who will fight, and together we will win. One of the most powerful companies in the world wouldn't be retaliating against us if collective action didn't work."
Follow Dave Lee on Twitter @DaveLeeBBC
Do you have more information about this or any other technology story? You can reach Dave directly and securely through encrypted messaging app Signal on: +1 (628) 400-7370