Internet giant Google has fired the male engineer at the centre of an uproar in the Silicon Valley over the past week after he authored an internal memo asserting there are biological causes behind gender inequality in the tech industry.

James Damore, the engineer who wrote the memo, confirmed his dismissal, saying in an email to the Reuters news agency on Monday that he had been fired for "perpetuating gender stereotypes".

Damore said he was exploring all possible legal remedies, and that before being fired, he had submitted a charge to the US National Labor Relations Board (NLRB), accusing Google upper management of trying to shame him into silence.

"It's illegal to retaliate against an NLRB charge," he wrote in the email.

The move, which was not officially confirmed by Google, splashed fuel on a burning controversy about whether "political correctness" at the company was stifling free speech.

Google told the AFP new agency that the company "can't comment on individual employee cases".

Memo 'violates Code of Conduct'

Google Chief Executive Sundar Pichai told employees in a note on Monday that portions of the anti-diversity memo "violate our Code of Conduct and cross the line by advancing harmful gender stereotypes in our workplace," according to a copy of the note seen by Reuters.

It was not immediately clear what legal authority Damore could try to invoke. Non-union or "at will" employees, such as most tech workers, can be fired in the US for a wide array of reasons that have nothing to do with performance.

The US National Labor Relations Act guarantees workers, whether they are in a union or not, the right to engage in "concerted activities" for their "mutual aid or protection".

Debate over the treatment of women in the male-dominated tech industry has raged for months. Claims of persistent sexual harassment in the ranks of Uber Technologies Inc and several venture capital firms have led to management shakeups.

Management at the largest tech firms, including Google, have publicly committed to diversifying their workforces, although the percentage of women in engineering and management roles remains low at many companies.

The US Department of Labour is investigating whether Google has unlawfully paid women less than men. The company has denied the charges.