Just days after becoming controller of financially strapped Harrisburg, Pa., in January, Daniel Miller began uttering an obscure term that baffled most people who had never heard it and chilled those who had: Chapter 9.

The seldom-used part of U.S. bankruptcy law gives municipalities protection from creditors while developing a plan to pay off debts. Created in the wake of the Great Depression, Chapter 9 is widely considered a last resort and filings under it are more taboo than other parts of bankruptcy code because of the resulting uncertainty for everyone from municipal employees to bondholders.