LGBT groups from the UK political parties have expressed "disappointment and anger" over potential changes to laws affecting trans people.
Leaders of the groups representing lesbian, gay, bisexual and transgender members directly addressed the minister for women and equalities in a letter.
They fear leaked plans show it could be harder for trans people to transition.
The government said it will publish its response to a consultation on the Gender Recognition Act in the summer.
The LGBT groups featured in the letter to Liz Truss, seen by the BBC, are from the Conservatives, Labour, Scottish National Party, Liberal Democrats, Plaid Cymru, Greens and Alliance parties.
The groups are concerned the potential plans will see the government amend laws to make it more complicated for trans people to transition and access facilities such as toilets and changing rooms.
The leak, first reported by the Sunday Times, stated that ministers have "ditched" plans developed under Prime Minister Theresa May to allow trans people to change their birth certificates without a medical diagnosis, and that "safeguards" will be put in place to "protect safe spaces for women," with amendments to the Equality Act.
Currently, the Gender Recognition Act requires trans people to go through a long process in order to change their birth certificates.
For this reason, many do not, and instead rely on the protection afforded by the Equality Act 2010. Gender reassignment is a protected characteristic under the Equality Act - to safeguard transgender people against discrimination and that can be based on self-identification alone.
The 2010 act says: "A person has the protected characteristic of gender reassignment if the person is proposing to undergo, is undergoing or has undergone a process (or part of a process) for the purpose of reassigning the person's sex by changing physiological or other attributes of sex."
The Equality Act also effectively permits service providers not to allow a trans person to access separate-sex or single-sex services—on a case-by-case basis, where exclusion is "a proportionate means of achieving a legitimate aim".
The government has not yet commented on the leak or its accuracy but should the plans go ahead as reported, the group warns it will be a "step backwards" for LGBT rights.
Colm Howard Lloyd, chair of LGBT+ Conservatives, says the current "toxic atmosphere" is leading to trans people fearing for their safety and future.
He said: "The minister for equalities has said that all trans adults should be free to live their lives as they wish without fear of persecution. The LGBT groups of all major UK parties call on the government to back that with action."
In 2018 the government launched a public consultation in order to understand gender in more detail and explore ways in which the system could be improved.
It acknowledged that many trans people find the current requirements "too bureaucratic, expensive and intrusive".
The consultation closed in October 2018.
A response was promised "by spring 2019", and then "before Parliament's summer recess" in 2019, but now an update is expected by the end of July.
A spokesman for the Government Equalities Office said: "We will publish our response to our consultation on the Gender Recognition Act this summer."
'Rollback on trans rights'
The cross-party letter says a "rollback on trans rights" could repeat "past mistakes" and requests of Ms Truss:
- To meet with the representative from the political coalition "to hear our position on trans equality"
- Rule out any revisions to the Equality Act and any restrictions to trans young people accessing healthcare
- Publish a timeline of the potential changes to the Gender Recognition Act.
Melantha Chittenden and Heather Peto, co-chairs of LGBT+ Labour, told the BBC they are prepared to work with colleagues from across the political spectrum to protect trans rights and they will fight the government's plans "every step of the way."
"It is a disgrace that we have waited two years for the government to announce long promised changes to the Gender Recognition Act only for them to go back on their word," they said.
The group say they hope that their cross-party coalition will stop this potential "reversal of LGBT rights".
"This is unique," say Benali Hamdache and Chandler Wilson, co-chairs of the LGBTIQA+ Greens, "it really shows the breadth of the political support for trans rights. We'd urge this matter to rise above party politics."
They added: "Trans people deserve respect and dignity, not harassment, marginalisation and vilification. Please Liz, do the right thing."
Josh Aaron Mennie of the SNP's LGBT wing, Out for Independence, added: "These are reforms backed by the LGBT affiliate organisations from every main political party in the country, I urge Boris Johnson to listen to us."
Currently to change their legal sex a person has to show they have lived in their new gender for two years and will continue to do so as well as getting a diagnosis of gender dysphoria from two doctors, she said.
Joan Smith, feminist writer and human rights activist, said: "'No-one has proposed to take away rights and protection from trans men and women - the situation is exactly as it was last week. It looks as though ministers intend to maintain the current system of regulation for the process of getting a new birth certificate, which is one of many processes regulated by the state.
"In April, Liz Truss talked about the importance of single-sex spaces, but that might simply mean clarifying the exemptions that already exist under the 2010 Equality Act. Many women welcome that as well, and I think its important to base this discussion on what's actually happened, instead of a very emotional species of speculation."
Clarification 22nd June 2020: This article has been amended to clarify the terms of the Equality Act 2010.