Should the employer be informed about an employee who agreed with a client to execute the company's projects outside of it, knowing that informing him might lead to the employee losing his livelihood, or should one remain silent about the matter while feeling guilty towards the employer?

The employee who agrees with a company client to execute private projects without the company's knowledge is considered a betrayer. He must repent and return the agreement and the amounts he obtained to the company, unless the company forgives him. If he does not do so, the questioner must inform the company about it, based on the hadith (definition): "Religion is [sincere] advice." There is no blame upon him for doing so, because he is preventing injustice and fulfilling the duty of advising the rightful owner.