The complaint was filed late Monday with the U.S. National Labor Relations Board (NLRB), according to No Tech For Apartheid, a group affiliated with some of the workers. The group said the complaint alleges that by firing the workers, Google interfered with their rights under U.S. labor law to advocate for better working conditions.

Reuters could not immediately obtain a copy of the complaint. Google did not immediately respond to a request for comment.

Google this month said it had fired 28 employees who disrupted work at unspecified office locations while protesting Project Nimbus, a $1.2 billion contract jointly awarded to Google and Amazon.com to supply the Israeli government with cloud services.

The workers claim the project supports Israel's development of military tools. Google has said the Nimbus contract "is not directed at highly sensitive, classified, or military workloads relevant to weapons or intelligence services."

Zelda Montes, a former Google employee who was arrested during a protest of Project Nimbus, said in a statement that Google fired workers to suppress organizing and send a message to its workforce that dissent would not be tolerated.

“Google is attempting to instill fear in employees," Montes said.

The workers in the NLRB complaint are seeking to be reinstated to their jobs with back pay, and a statement from Google that it will not violate workers' rights to organize.

The NLRB general counsel, which acts as a prosecutor, reviews complaints and attempts to settle claims it finds to have merit. If that fails, the general counsel can pursue cases before administrative judges and a five-member board appointed by the U.S. president.