By a community meal:[1]

Some Poskim^[2] rule that from the letter of the law, there is room to be lenient to have a public meal without a Mechitza between the men and woman side. However, according to the Rebbe’s directives, a public meal is to have a Mechitza in-between the men’s and women’s section.[3]

Purim Seuda: Certainly, there should be a Mechitza present between the men and women by a community Purim meal, as there is great joy and drinking of alcohol which takes place, and is hence similar to a wedding meal in this regard.[4] The widespread custom, however, is to not require there to be a Mechitza between the men and women by a private Purim meal. Nonetheless, the men and women are to sit by different sides of the table.

Shul or Chabad house meals: Many are accustomed to not require there to be a Mechitza between the men and women by a public meal held in a Shul on a typical Shabbos or holiday. Nonetheless, the men and women are to sit by different sides of the table.

Banquet or Dinner events for institutions: Many are accustomed to not require there to be a Mechitza between the men and women by a dinner event. Nonetheless, some are meticulous to do so and have a Mechitza between the men and the women[5] and so is the accepted practice amongst Charedi Jewry in Eretz Yisrael, with some Poskim[6] ruling that it is an absolute requirement. According to all, it is improper for there to be mixed seating and hence at the very least, the seating for the men and women should be separate.[7]

Public Pesach Seder:[8] The widespread custom is to not require there to be a Mechitza between the men and women by a public meal held by a public Pesach Seder. Nonetheless, the men and women are to sit by different sides of the table.

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[1] The Rebbe’s position: Rabbi Groner relates that he had did not hear anything directly from the Rebbe regarding whether a Mechitza is necessary by community meals.

[2] Igros Moshe O.C. 1:41 “In an area of gathering of Davar Reshus, I question whether there is a prohibition and I more lean to say that there is not”; Y.D. 4:24-3 “A wedding is a private event, and a Mechitza is only needed by a public event”; However, see Igros Moshe O.C. 1:39 in which he states that all areas designated for gathering require a Mechitza and does not differentiate between Reshus and Chova or Mitzvah, and only differentiates between Makom Kibbutz and non-Kibutz

[3] See Hiskashrus 588:11;

[4] So ruled to me: Rav Eli Landa Shlita; Rav Michael Avishad; Rav Shaya Braun; Rav Yosef Simcha Ginzberg; Rav Aaaron Yaakov Shwei

[5] Rabbi Groner relates that Rav Michael Teitelbaum of Ohalei Torah was the only one he remembers was particular to have a divider by the dinner for the Yeshiva Ohalei Torah

[6] Lev Avraham 1:135

[7] Response of Rebbe to Mosad, brought in Devar Melech p. 127 “why push away a definite matter of fear of heaven of all those present due to a question about money of the few individuals”

[8] See Pesachim 64b; 86a; 91a that the law is that it is forbidden to have a Mechitza present between the group of people who would eat the Pesach sacrifice on the night of Pesach.