Google unlawfully fired employees for attempting to organise a union, a US federal agency has said.

A complaint filed by the US National Labor Relations Board (NLRB) alleged that Google unlawfully monitored and questioned its employees about their union activity.

It fired a number of staff for violating data security - but the NLRB said the rules were applied only to those engaging in union activity.

Google denies doing anything unlawful.

Google fired employees for union activity, says US agency https://t.co/bga5Pg1fPv

— BBC News Technology (@BBCTech) December 3, 2020

It comes as another prominent Google employee, a leading figure in AI ethics, said she was fired for an email she sent to employees.

The NLRB complaint dealt with employees who were fired over a year ago, in November 2019.

Known as the "Thanksgiving Four", they were officially fired for breaking security and safety rules. But the workers alleged they were fired for "speaking out" about Google's policies.

Reacting to the NLRB complaint, Google said it had "always worked to support a culture of internal discussion".

"Actions undertaken by the employees at issue were a serious violation of our policies and an unacceptable breach of a trusted responsibility," it said.

But the NLRB said the rules in question were only applied to those employees who were engaged in worker organisation.