Membership

Hi,

Rav Moshe Feinstein ruled that a Jew may not be a member of an organization whose activities include Shabbat desecration [by Jews, presumably]. Although he does not violate Shabbat, he supports the Shabbat desecration by others via his membership.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 2:61)

Have a great day,
Mordechai