Municipal bonds have traditionally had very low rates of default as they are backed either by revenue from public utilities (revenue bonds), or state and local government power to tax (general obligation bonds). However, sharp drops in property valuations resulting from the 2009 mortgage crisis have led to strained state and local finances, potentially leading to municipal defaults. For example, Harrisburg, PA, when faced with falling revenues, skipped several bond payments on a municipal waste to energy incinerator and did not budget more than $68m for obligations related to this public utility. The prospect of Chapter 9 municipal bankruptcy was raised by the Controller of Harrisburg, although it was opposed by Harrisburg's mayor.