Cathay Pacific is investigating rumours of an anonymous letter purportedly written by staff members expressing support for anti-government protests in Hong Kong.

“While we cannot confirm the authenticity of this letter, we are taking the matter very seriously and are conducting an internal investigation,” the Hong Kong carrier says.

According to the South China Morning Post, the letter criticised the Hong Kong government for its response to protestors.

The letter also called out the Civil Aviation Administration of China’s move to issue a major safety risk warning to Cathay, calling it “white terror” against freedom of speech.

The CAAC notice said that all Cathay employees who supported "illegal protests and violent acts" in Hong Kong "must be immediately suspended from serving any mainland-bound flights or any other transportation activities involving the mainland". The carrier has also been forced to submit the identity of all crew operating on flights to China.

Cathay, in its latest statement, also reiterated its support for the Hong Kong government, the Hong Kong chief executive, and the police force, which has been criticised for its use of excessive action against protestors.

The Oneworld carrier has faced intense scrutiny from China in recent days, culminating in a major senior management shake-up on 16 August.

Cathay’s former chief executive Rupert Hogg and his deputy, ex-chief customer and commercial officer Paul Loo, both announced their surprise departure from the airline, citing the need to “take responsibility” as its leaders.

Cathay has also fired two pilots and two ground staff for their involvement in the protests, which stem from the government’s plan to introduce an unpopular extradition bill.