“And you shall not bear a sin because of him!” (Vayikra 19:17)
It is a negative commandment, that one may not embarrass a member of Klal Yisrael. This sin is named in the words of Chazal “whitening one friend’s face in public”. The source of this prohibition is the following. The Torah commands us “You must surely rebuke your friend!”. One might think that one must rebuke him even if he will become embarrassed and his face will change color? The Torah stipulates however, that “And you shall not bear a sin because of him!”.
The root of this commandment is known, for embarrassment is the ultimate pain for a creature. Because of this, Hashem forbade us to hurt His creatures in this way, for one can rebuke them privately and the sinner will not be as embarrassed.
Chazal warned us that in regards to this prohibition, it would be better for a person that he should throw himself into a fiery furnace rather than publicly embarrassing his friend. This is extrapolated from the story of Tamar the daughter-in-law of Yehudah, who did not wish to publicly embarrass her father-in-law, and if not for the fact that she found the pledge and made the facts known to him through an allusion, she would have been sentenced to be burnt rather than embarrass him.
This commandment applies in all places and at all times. One who publicly embarrasses his friend has transgressed the command of the King, and Hashem has many messengers to pay back those who go against His will.