From Longman Dictionary of Contemporary Englishbite the hand that feeds youbite the hand that feeds youHARM/BE BAD FORto harm someone who has helped or supported you → bite
Examples from the Corpus
bite the hand that feeds you• If I put my prices up, it's like biting the hand that feeds me - it's economic suicide.• It is hard to bite the hand that feeds you.• Somehow, without guidance and peer influence, cricketers are apt to bite the hand that feeds them.• They are not normally going to bite the hand that feeds them.• This appears to be a new version of biting the hand that feeds you. 