A. Yisod Veshoreash Hoavodo (Shaar 9: 11) mentions that the twentieth of Sivan became a day of fasting due to the many tragedies which began on that day.
On the 20th of Sivan (1171) - The first blood libel in France - tens of Jewish men and women including three great tzadikim, were burned alive in the French town of Blois because of the accusation that Jews used the blood of Christian children in the preparation of matzah for Pesach.
The Shach was from the first who instituted this day as a fast day, commemorating the “Gezeiros Tach V’Tat,” (the catastrophic Chmielnicki massacres in Southern Poland and the Ukraine in 1648-1649). It would seem, however, from his own words, that he had established the fast day only for his family and descendants. This would explain why, in 1652, the Vaad Arba Hoarotzos (Council of the Four Lands) also declared a fast on 20 Sivan; they were establishing one for the public at large. It became accepted mostly in Poland. (Taz O.H. 566)
Mishna Berura (566: 10, 574: 2) mentions in regards to the reading of Vayechal, that the 20th of Sivan in his days became less established as a day of fasting, and only a few observed it. He also, by quoting Mogen Arohom and Pri Megodim, debates about eating at a bris mila or other seudas mitzva on that day and what to do on Erev Shabbos.
Horav Shlomo Miller's Shlit'a opinion is that today the twentieth of Sivan is not a well known occasion at all and the minhag for most is not to fast or say selichos. Therefore, one may attend the wedding of a close friend and comply with the biblical mitzvah of rejoicing with the chosson and kallah.
There is also no need to search for a minyan that says selichos, which may be hard to come by, unless one has a family tradition to do so.
Rabbi A. Bartfeld as revised by Horav Y. Hirshman, Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu, Horav Kalman Ochs, and Horav Dovid Bartfeld consulting in need Horav Hagaon Rav Yitzchak Berkowitz Shlit’a
Important Numbers
