La Línea owes banks €100 million and fell behind in salary payments to municipality employees over the summer. About 10,000 of its 65,000 inhabitants are unemployed, compared with 4,000 jobless five years ago.“The boom years created jobs, but when the building craze suddenly ended, there was no obvious way to channel all these people into other activities,” Mr. Sánchez said. “We’re now told by Madrid that we cannot take on more debt, but that puts a city like ours in an impossible situation.”In Jerez de la Frontera, a municipality known for its wine and flamenco, the debt pile has reached €670 million, or about $883 million. The economic slowdown has also cut Jerez’s tax revenue to €11 million last year from €41 million in 2008. “I’m running a war economy,” said Jerez’s mayor, Pilar Sánchez.The...