There are some grounds for a more immediate removal from either a
congregation or the communion of a whole ecclesiastical body, without
attempting first to seek redress from church judicatories (in
addition to what has been noted above by McCrie, etc.), as in (this
list pretends not to be exhaustive, only examples that I think would
tend in that direction):
when a church professes more, less, or different persons of the
Godhead or such like Trinitarian / Christological errors.
When a church introduces rites and ceremonies and requires that they
be interpreted as acts of worship. Note Clarkson mentioned that
vestments were borne with during a time of reform, and Bullinger's
advice to Hopoper not to forsake the church for caps and gowns is
famous. Yet, as Bullinger expressed his grave misgivings (somewhere -
I forget the reference, but it was in a letter addressed to some
British divines) that some in the church were beginning to press that
the vestments be not only worn, but understood as worn as an act of
worship. If it be required upon the conscience of the believer that
it be an act of worship, there may be cause for immediate separation,
though perhaps only from the assembly while attempting yet to press
the matter thru the courts of the church. There have been times in
the beginnings of such things (as in Holland in the 1800s) when there
may be cause for nonparticipation with certain acts (during the
controversy in question, it was not uncommon for a segment of the
church to march out of the service during the offending part, and
walk back in when it was over - ouch!). However, if one stays, it
would seem to me that they are duty bound to seek that the matter be
addressed by the courts of the church and not simply atempt to
preserve the status quo or introduce their own ideas on a private
level to be dispersed thru a congregation person by person without
being brought up before the officers and courts of the church.
When a church outlaws the gospel.
When a local assembly brings in a heresy contrary to the gospel, but
one that has never yet been considered thru the church, it may be
needful to separate from that local assembly while addressing
concerns to the judicatories, in order to flee with your children
from being taught a false gospel.
When a church has communion with that man of sin after he has been
revealed, the reformers were clear they needed to separate. The
Lutherans also made clear that they would hold no joint counsel with
the other churches if the papacy was regarded as having any authority
in or over the council.
There may be other reasons as well.
Last post on this.