Employer cheating the customers

I am working in Singapore. I am in charge for some oil carrying ships of a company. I would prepare the ships technically to run smoothly. But I don't involve myself in the operation department. But my boss cheats the customers by supplying oils short. For eg: instead of 5000 MT, 4600 MT will be supplied through the help of the operation department. Kindly advise whether my earnings are halaal? Though I am not involved myself in these activities, I feel that my earnings are haraam and my duas will not be accepted.