不食周粟

Etymology
(approximately 1046 BCE), two princes of the former, refused to eat the food of the newly founded (in their opinion, usurping). They lived in seclusion in Shouyang Mountain and ate fiddlehead ferns before starving to death:

Idiom

 * 1)  to refuse to eat the food of the Zhou dynasty
 * 2)  to categorically refuse to cooperate with people or actions that one disagrees with out of his/her conscience or loyalty