My father is a Policeman. So he gets his salary from the government. But the government gives the salary from collecting tax from its citizens which can include tax from haram companies like alcohol producers. Simply some money from haram sources go to government and my father earns them from government. So is my father's and all other government employees' earning also haram?
Your father's work is for the government if he does his work well he surely should receive and accept the payment as a halal income.
In Islam the source of money is secondary while what is more important is to earn it by your own effort and in a halal manner (halal job, without doing anything sinful or wrong in this job).
Note that taxes are halal as long as they are fair and have a clear general benefit, be it educational or hygienic or... For details see Is there a difference between taxes and customs in Islam?