Public bodies, as well as security and law enforcement agencies, may access selected personal data from the population register under certain conditions. Further information is available here.
You can block wage tax deduction features (tax class, child allowances) by notifying your tax office. Your employment company will then tax your wages according to tax class VI.
There are many circumstances that cause a change in the wage tax deduction criteria for the employee or make it necessary (e.g. marriage, birth of a child, joining or leaving church). These changes are implemented in the ELStAM procedure ...