What is the ruling on an employee's knowledge of their manager's corruption at work, represented by giving some employees unjustified additional wages, and what are the consequences for them if they fear reporting it?

If your manager pays wages to those who do not deserve them, this is consuming people's wealth unlawfully, based on the Almighty's saying: "And do not consume your properties among yourselves wrongfully." You must advise him in a good manner, and if he does not respond or you fear harm, then inform higher authorities of what is happening, even if indirectly, based on the Prophet's (peace be upon him) saying: "Religion is advice."