daily word - justice and mercy

Do you know the difference between justice and mercy? Justice is deserved and can be claimed; mercy is a benevolent gift. In my word I refer to justice for the poor. Do you see it as justice or mercy? Most who donate would count it as an act of charity, alms-giving, or philanthropy. Who thinks of this as justice? In like manner, is it possible for there to be unfair labor practices if the terms of employment are accepted voluntarily? But I make it clear that I do not approve of defrauding the worker of his wages. Justice is a stronger term than mercy. So why do I refer to justice for the poor rather than mercy?