Sports teams, pride event organisers, national organisations and local support groups have united to declare their commitment to trans equality as the government consults on the controversial proposed legal changes.
On reform of gender recognition, the letter states: "We stand in support of a reformed Gender Recognition Act that enables trans people to more smoothly change their birth certificates to match their lives and other identity documents."
The letter also hits back at the creation of a new organisation, the LGB Alliance, which has said it is concerned that trans rights are undermining the idea of homosexuality, and supports the Scottish Government's current plans for LGBT inclusion in the 2021 national Census.
"In all our progress, in working towards our shared goal of equality for all, we have proudly recognised and valued the range of needs and priorities within our diverse community. Recently, we have been concerned by attempts by some to isolate the trans community from the wider LGBT community; this goes against everything we stand for.
"Trans people are the women, men, and non-binary people that they say they are. We are resolute and united in support of trans equality and human rights, as we have always been, and today reaffirm our support for trans people and equality.
"We stand for LGBT equality alongside equality for all other groups - there is no real equality unless it is equality for all."
The new LGB Alliance, whose founders include Simon Fanshawe, one of the orginators of Stonewall, had its first Scottish meeting last weekend, and launched a newspaper advert campaign against the proposed reforms to the GRA. The group believes that "transgender theory", invalidates same-sex attraction, and undermines women's rights to single-sex spaces such as changing rooms, toilets, refuges and even prisons.
However, one of the signatories, Stuart Duffy, founder of Pink Saltire, said: "This unprecedented demonstration of support and solidarity from LGBT organisations right across Scotland sends a clear message that we will not be divided on this issue.
"Trans and non-binary people have been, and continue to be, absolutely critical in the fight for LGBT equality and we will not abandon them or deny their existence as others would - we stand shoulder to shoulder and resolute in our support."
And Dr Rebecca Crowther, policy co-ordinator at the Equality Network, added: "We know that an overwhelming majority of the LGBT community support trans equality. The LGBT groups and organisations that have signed this letter prove just that.
"It is vital that the LGBT community and allies continue to stand together to ensure that Scotland continues to be a progressive and inclusive country for all and that this is reflected in policy and legislation."
The Census questions are currently being reviewed by a Holyrood committee, and concerns have been raised about allowing transgender people answer the sex question in their "lived gender" rather than their biological sex. The Census will also offer a voluntary question for people to state their trans status.