San Francisco (AFP) - Four employees fired by Google ahead of the Thanksgiving holiday said Tuesday they were seeking a federal investigation into their dismissal, which they claimed was in retaliation for their labor organization efforts.

The dismissal of the group dubbed the "Thanksgiving Four" on social media highlighted deepening tensions at Google, which had stated the employees violated data security policies.

A Medium post signed by the four said Google "fired us for engaging in protected labor organizing" at the Silicon Valley giant.

"We spoke up when we saw Google making unethical business decisions that create a workplace that is harmful to us and our colleagues," said the posting signed by engineers Laurence Berland, Paul Duke, Rebecca Rivers and Sophie Waldman.

"We participated in legally protected labor organizing, fighting to improve workplace conditions for all Google workers."

The four said they would file a complaint alleging unfair labor practices with the National Labor Relations Board.

"We look forward to hearing the NLRB's findings, which we expect will confirm that Google acted unlawfully," they said.

The dismissed engineers said they were acting on the basis of Google's own internal rules.

"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," they wrote.

The posting said the employees were seeking better conditions for temporary and contractual workers, challenging the protection of executives accused of sexual harassment, and organizing around topics such as gender discrimination and Google's projects involving the US and Chinese governments.

Google, the biggest operating unit of parent company Alphabet, said in a memo to employees that the dismissals were based on unauthorized access to data from other employees and sharing that information externally.

The tech giant denied the employee allegations.

"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," a Google statement said.

"No one has been dismissed for raising concerns or debating the company's activities."