If this was a government censoring, banning journalists, stories and the media or even blocking the whole internet and punishing companies that criticize them or to stop the letter being published, that totally violates free speech.

Generally, It doesn’t apply to ‘privately owned companies’ Just like how these employees are free to criticize their employer it does not mean there are freedom of consequences and employers are just as free to fire their employees.

That is why they stay anonymous and criticize their employer just like what happened with Coinbase.