This multi-part series is well worth a read. Here's a flavor from the summary:
Debt collection horror stories are nothing new. But there's a whole other side to the industry that no one’s talking about: collectors hired by government agencies to hunt down debtors….
[G]overnment debt collectors are rarely held to the same consumer protection laws as collectors that go after credit card debt or auto loans. And with the power of state and local governments behind them, these debt collectors can charge steep fees and make scary threats, warning that the government will suspend your driver’s license, garnish your wages – even issue a warrant for your arrest.
Go here for the main page, which includes a summary and links to stories on different aspects of the problem.