Under federal legislation like the Fair Debt Collection Practices Act, debt collectors are legally prohibited from using abusive, deceptive, or harassing tactics. The worst lawful actions a collector can take include filing a formal civil lawsuit against a debtor in court, obtaining a legal judgment, and subsequently garnishing wages, freezing bank account funds, or placing liens on real estate property. They can also report severe delinquencies to major credit bureaus, which significantly damages credit scores.