The meaning of mulct is as nasty as it sounds; it means to fine someone or the money you collect as a result of a fine. No one wants to pay an extra mulct to the city, when it's the city who mismanaged the budget.
Got mulct? Then somebody took your money. They "milked" you by mulcting you. And the money that they took? That's called mulct, too. Some people believe that there's no difference between being mulcted by the state and being shaken down by the mob. In fact, the word mulct is often used to mean having your money taken unfairly or as a kind of punishment or as extortion.