Leading figures in the Church of England are set to debate homosexuality and same-sex marriage.
Peaceful protesters - led by the former bishop of Worcester - have gathered on the steps of Westminster's Church Hall, London, in support of LGBT rights within the Church.
A report by the House of Bishops calls for the Church to adopt a "fresh tone and culture of welcome and support" for gay people - but not to change its opposition to same-sex marriage.
Campaigner Peter Tatchell said he was "appalled" by the church's treatment of LGBTI people.
He said: "The Bishops' report defends heterosexual superiority and opposes same-sex blessings and marriages.
"The church blesses dogs and cats but it refuses to bless loving, committed same-sex couples.
"It treats LGBTI clergy and laity as second class, both within the church and the wider society."
The Rt Rev Dr Peter Selby, one of the letter's supporters, added: "Our perception is that while the pain of LGBT people is spoken about in your report, we do not hear its authentic voice.
"Our experience would lead us to doubt whether there was an expectation around that canons and doctrinal statements would be changed within any reasonable timescale, and that focus seems to have taken far more time than it would have done if the authentic voices of lesbian and gay people had been allowed to express the major focus of their hopes."
The report, which was published last month, will be the subject of a "take note" debate as more than 400 Church leaders gather for the third day of the Synod at Church Hall in Westminster, London.
This means the Synod will discuss the content and recommendations of the report to inform future work, but the proposals will not be formally rejected or approved.
The Lesbian and Gay Christian Movement has said the proposals would "formalise Don't Ask, Don't Tell among clergy in same-sex relationships" - a claim the Church has rejected.
The term is a reference to the former US military policy between 1994 and 2011 which barred openly gay or bisexual Americans from serving but did not discriminate against them if they did not disclose their sexuality.