I teach my students that the days of the debtor's prison and the workhouse are long past; the only debt you can go to prison for are domestic support obligations.  But it turns out that there's another jailable offense:  failing to pay the court.  The New York Times has a story about Florida's practice of issuing writs of bodily attachment or "blue writs" for failure to appear in court.  The jail time under one of these writs is supposed to be at most 48 hours (plus a $20 fine!), but a study by the Brennan Center for Justice at NYU found that some individuals were imprisoned longer.  Florida's state constitution (like many other state constitutions) specifically forbids imprisonment for debt (excluding fraud), and there's a line of US Supreme Court cases holding that the Equal Protection Clause bars imprisonment solely because someone is unable to pay a debt. 

Technically it is jail time for failure to comply with a court order (much like failure to comply with a domestic support obligation); in that sense it's just plain old civil contempt.  But the wide-scale use of civil contempt to force payment for court fees strikes me as novel.  It's certainly been used before to effectuate things like turnover orders, but there's something very awkward about the courts in the role of creditor.