at the expense of

1. To the detriment or injury of a person or thing, as in We can't speed up production at the expense of quality , or The laughter was all at Tom's expense . [Late 1600s]

2. Paid for by someone, as in The hotel bill for the sales force is at the expense of the company . [Mid-1600s]

Idioms and Phrases

Also, at one's expense .