IMHO.....Do not even think about as it most likely will come back to the company, TA and client who is paying....use your miles for personal travel or upgrade on your dime. But hey put your self in your company's shoes...What would you think of an employee who did this? But that's just me talking . My job is way to important to even contemplate the thought. I would love to see that expense report and possibly an audit. I highly doubt your boss would take kindly on this and yes it ain't worth your job. Read your company's travel policy. Personally I wouldn't do it unless of course you had written permission and yes what about tax consequences? There are other ways to earn miles, but this isn't Kosher unless you put the cards on the table upfront.