A group of workers at Alphabet Inc's Google have filed a complaint with a U.S. labor board claiming the tech company unlawfully fired about 50 employees for protesting its cloud contract with the Israeli government.

The single-page complaint filed late Monday with the U.S. National Labor Relations Board (NLRB) alleges that by firing the workers, Google interfered with their rights under U.S. labor law to advocate for better working conditions.

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 company last week said that about 20 more workers had been fired for protesting the contract while in the office.

In a statement on Tuesday, Google said the workers' conduct was "completely unacceptable" and made other employees feel threatened and unsafe.

“We carefully confirmed and reconfirmed that every single person whose employment was terminated was directly and definitively involved in disruption inside our buildings," the company said.

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 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 in a statement provided by No Tech For Apartheid, an organizing group affiliated with some of the fired workers.

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.