Is it permitted to daven in a shul in which the mechitzah allows men to see into the ezras nashim? In other words, is a glass mechitzah permissible?

An all-see- through- glass mechitza that separates the women’s section from the men’s section when both are on ground level (when the women are not in a raised balcony on a second story) is insufficient. The mechitza according to HaRav Moshe Feinstein must fulfill two requirements: 1) it must prevent any intermingling or levity between men and women and 2) it must be a barrier between the men and those women who may come to shul dressed in a way that is inconsistent with the laws of modesty. A mechitza that consists of a lattice-work that allows men to see into the ezrat nashim only with difficulty and prevents cross-mechitza discussions is, however, acceptable (Iggrot Moshe Orach Chayim I 43 and Orach Chayim III 23).