Teachers" Union v. City Hall Since taking office in 2002, Mayor Michael Bloomberg has pursued an aggressive policy of replacing large, failing schools with smaller, specialized ones and greatly expanding the number of charter schools, which receive public money but are exempt from some state rules. In all, Mr. Bloomberg has shut down or begun to phase out 142 schools. In addition, the city now has 159 charters schools, up from just 17 when he took office. This policy has improved educational quality in many poor communities. But it has angered some community groups and the teachers" union. The union went to court last month to challenge a plan that would open new schools or expand existing ones in 13 school buildings well after Mr. Bloomberg leaves office. The union is especially concerned about new or expanded charter schools, which are generally not unionized and which typically require space in buildings that are already occupied by traditional public schools. The suit argues that by drawing up a plan in advance, the administration has effectively closed off debate on the space issue before the public can weigh in. But the next mayor is not bound by the current mayor's policies. The suit's underlying point seems political: to send a clear warning to Mr. Bloomberg's successor that the union wants a new set of policies. Mr. Bloomberg rightly believes that shutting down failing schools and expanding the highest-performing charter schools are critical elements in any broader school reform. The union believes that things have gone too fast, and means to press the point.