If you refer to someone as a hireling, you disapprove of them because they do not care who they work for and they are willing to do illegal or immoral things as long as they are paid.
[disapproval]
hireling in British English
(ˈhaɪəlɪŋ)
noun
derogatory
a person who works only for money, esp one paid to do something unpleasant
Word origin
Old English hӯrling; related to Dutch huurling; see hire, -ling1
hireling in American English
(ˈhaɪrlɪŋ)
noun
1.
a person who is for hire; esp., one who will follow anyone's orders for pay; mercenary
adjective
2.
of or like a hireling; mercenary
Word origin
hire + -ling1
Examples of 'hireling' in a sentence
hireling
He was dogged by government hirelings who hissed and hooted at him on every public occasion.
Adam Sisman The Friendship: Wordsworth and Coleridge (2006)