Google is currently under a federal investigation held by the US National Labor Relations Board that must determine whether any formal actions need to be taken. It will also consider whether Google discouraged its employees from taking part in union activities. The federal complaint was filed on December 5.

A probe is being opened following the complaint about the company’s labor practices made by four former employees who were fired. The investigation is estimated to take about 90 days and will be conducted by the Oakland staff.

The fired employees are software engineers Rebecca Rivers, Paul Duke, Laurence Berland, and Sophie Waldman. In the complaint, they accuse Google of “unlawful conduct” when firing the employees that wanted to make their working conditions at the company better.

Last month, Google fired the “Thanksgiving Four” (the people are called this way because they were dismissed right before the Thanksgiving holidays) allegedly for sharing confidential information and therefore threatening the company’s security. However, this happened right after several hundreds of Google employees held a protest outside the company’s San Francisco office because of the decision two fire two employees.

As Google spokesperson said in a statement:

We dismissed four individuals who were engaged in intentional and often repeated violations of our longstanding data security policies, including systematically accessing and disseminating other employees’ materials and work. No one has been dismissed for raising concerns or debating the company’s activities.

The “Thanksgiving Four” has public support from such political figures as Bernie Sanders and Elizabeth Warren. All of them were internal activists of the company who invited other workers to join protests against Google’s questionable decisions for the future or, as the fired employees say, “Google was making unethical business decisions that create a workplace that is harmful to us and our colleagues.”