Last summer, Jessie Sander had been on the job at a Jewish school in Westchester County for less than a month when a meeting with her boss took an unexpected turn. Was she comfortable working at a Zionist institution? he asked. Her boss, Rabbi David E. Levy of Westchester Reform Temple in Scarsdale, N.Y., had come across a recent blog post she had written that renounced Zionism and sharply criticized Israel, Ms. Sander, 26, said in a lawsuit filed on Jan. 25. The rabbi had questions: Did she support Hamas? When she called herself "anti-Zionist," what did that mean?