6495 – Prohibition of Microphone Use on Shabbos and Yom Tov in Synagogue – איסור שימוש במיקרופון בשבת וביום טוב בבית הכנסת

The Rebbe writes that using a microphone on Shabbos and Yom Tov constitutes public desecration of these holy days, raising doubts about all prayers and Torah readings in such a synagogue. He advises praying alone rather than in a synagogue where this occurs.

https://www.torahrecordings.com/rebbe/igroskodesh/017/012/6495