Google (GOOGL  ) is under investigation by the National Labor Relations Board for its labor practices after the questionable firing of four employees on Thanksgiving that drew a great deal of scrutiny to the tech giant.

The NLRB confirmed on Monday that it was launching a probe into Google following allegations of unfair labor practices. The catalyst for the probe was the Thanksgiving firings of four Google employees, whom, according to google, were dismissed for "(engaging) in intentional and often repeated violations of our longstanding data security policies, including systematically accessing and disseminating other employees' materials and work."

The fired employees, however, disagreed with Google's statement. The employees, in their complaint to the NLRB, allege that they were instead fired for attempts to unionize and for their personal views against Google's actions, which included disapproval of Google's intent to create a censored version of its titular search engine for China and its contracts with the pentagon. The "Thanksgiving Four" raised concerns over numerous other practices at Google, including the treatment of contractors, cover-ups of sexual assault by executives, and retaliation against employees who registered complaints about their treatment.

"We've all been subjected to interrogations, some of us for hours, and all of us had our reputations smeared in the press as Google spread rumors that we were rule-breaking troublemakers who 'leaked' sensitive information" the four wrote, in reference to their treatment, and addressing Google's statements regarding their firing. "This is flatly untrue, and in the privacy of our meetings with HR and Google's internal investigations team, the company acknowledged this. A careful reading of their statements will only confirm this."

The NLRB will investigate Google's practices, with specific attention to whether or not the company violated the rights of the recently fired workers, and whether or not Google attempted to prevent workers from unionizing. Interestingly enough, the investigation into potential union-busting follows a bombshell report by the New York Times exposing Google for hiring a consulting firm that specializes in union-busting.

The controversy surrounding Google's treatment of its workers comes in the wake of previous investigation by the NLRB last year that looked into allegations by an ex-employee that Google restricted his free speech and fired him for his political leaning. Google settled with the NLRB but never admitted to any violations.