Further to your letter of 5 September 1974, the Universal
House of Justice has now had an opportunity to consider your question about
believers attending weddings of Bahá'ís who are marrying contrary to Bahá'í
law, and we have been asked to convey to you the following.
If it is known beforehand that a believer is violating such
laws, it would be inappropriate for the friends to attend the ceremony. This is
out of respect for Bahá'í law. However, if without realizing the situation
believers find themselves in attendance at a ceremony in the course of which it
is apparent that such a violation is occurring, they should not make an issue
of it.
- The Universal House of Justice (From a letter dated November 11, 1974
to a National Spiritual Assembly; compilation: Guidelines for Local Spiritual
Assemblies [Developing Distinctive Baha’i Communities], NSA of USA, 1998
edition)