The Archbishop’s letter, sent last February to state legislators on the finance committee, probably caught many Wisconsin Catholics off-guard. The fierce debate over stripping collective bargaining powers had so far been largely framed in economic terms: Were labor rights and a balanced state budget mutually exclusive? Citing Pope Benedict’s 2009 encyclical Caritas in veritate as evidence, Milwaukee Archbishop Jerome Listecki made the case that Wisconsinites ought to view the conflict through a religious lens. “Hard times,” Listecki wrote, “do not nullify the moral obligation each of us has to respect the legitimate rights of workers.”

Nor was Listecki’s letter an isolated event. United Methodist Bishop Linda Lee wrote an open...