In a related question, I cited a very interesting article by Dr Eli Turkel in Tradition (The nature and limitations of rabbinic authority). He writes there (pp. 83-84)
[…] community leaders only have religious authority if they are
followed by a majority of the community […] In modern times, no
single organization is accepted as authoritative by al Torah observant
Jews and, as a result, no group has the right to impose its views on
individuals who do not voluntarily accept them. […] Hence we
conclude that a modern rabbi’s authority is limited to his immediate
community or to those people who ask his opinion. No rabbi has the
right to impose his views on anyone else. (see also bottom of p. 86)
In conclusion he writes (p. 95)
We have shown that in the absence of a Great Sanhedrin, a court […] or
even a gadol hador can impose their halakhic opinions only if they are
accepted by the majority of a community. Even in that case, the
decisions affect only that specific community and not others.