Qitzur Shulchan Arukh – 183:3
Similarly, if the king’s army enters the city and the people of the city are obligated to provide them hospitality, one is prohibited to pay off the general of the troups to get him out of it. Because through this he will cause damage to someone else. Similarly in all other matters of taxes, it is prohibited to make efforts by the general to release him, if through this [the tax] will be heavier on others. And one who does this is called an “informer”.