The fresh controversy comes with Silicon Valley struggling in the face of accusations of rampant sexual harassment and discrimination affecting startups like Uber and venture capital firms investing in the sector.

Google chief executive Sundar Pichai, without commenting on Damore, said employees have a right to express themselves but that the memo appeared to "cross the line by advancing harmful gender stereotypes in our workplace."

Damore's 10-page memo, which was leaked on the website Gizmodo and later on Motherboard, argued that Google has silenced anyone seeking to differ with official policy, leading to "an ideological echo chamber."

Roger Kay, who heads the tech consultancy Endpoint Technologies Associates, said the Damore case is not about free speech, and that Google has a right to keep employees who support the company's values.

"Despite the broad official push for Diversity from tech companies, there's still a big chunk of the employee base that holds such views and wishes they could air them more freely."