LGBTQ organizations sent out a public letter on Monday to President Donald Trump’s administration making a single plea: Please keep a guidance, from the previous Obama administration, that protects transgender students’ rights in public schools.

The letter, from major LGBTQ advocacy groups, argues:

These guidance documents, addressing important issues such as sexual violence prevention and response, bullying and harassment, and the needs and rights of transgender students, provide practical answers to schools on issues they face every day. Each of these guidance documents is based on years of careful research to accurately reflect a substantial body of case law and proven best practices from schools across the country. Most importantly, these guidance documents have been instrumental in providing schools with the tools they need to protect the health, safety, and educational opportunities of millions of students.

(Read the full letter at the National Center for Transgender Equality’s website.)

A few months before Trump was elected president, the Obama administration sent out guidance to federally funded schools arguing that trans students are protected by existing federal civil rights law. So, the administration said, schools should respect trans students’ rights, including their right to use the bathrooms and locker rooms that align with their gender identity.

The Obama administration cited Title IX, which prohibits sex discrimination in public schools. It argued that anti-trans discrimination is prohibited sex discrimination, because discrimination against trans people is rooted in stereotypes and prejudices of what people should be like based on the sex they were assigned at birth.

But Trump said the guidance, even though it was not legally binding, was an example of federal overreach, and he vowed to undo it once he was elected. And last week, his Justice Department pulled away from a case defending the guidelines in court — suggesting that the Trump administration is ready to let the guidance legally die.

The guidance is important not just because of what it says about trans students in schools, but what it says for federal civil rights laws and trans people more broadly. Through this guidance and other actions, the Obama administration took a widely welcoming interpretation of federal civil rights law to include trans people. If the Trump administration ditches the guidance and other policies, it would effectively end an interpretation of federal law that gives trans people protections they otherwise don’t have in much of the country.

The Obama administration’s guidance was trying to clarify a key dispute in civil rights law

Under most states’ laws and federal law, trans people are not explicitly protected from discrimination in the workplace, housing, public accommodations, and schools. This means that a trans person can be fired, evicted, kicked out of a business, or denied the correct bathroom facility just because an employer, landlord, business owner, or school principal doesn’t abide by or acknowledge the trans person’s gender identity.

The Obama administration, under the urging of LGBTQ groups and a federal agency that works on workplace discrimination, adopted a different view of the law. It argued that federal civil rights laws do protect trans people in the workplace, housing, and schools.

The argument: Federal civil rights law already prohibits sex discrimination. And the ban on sex discrimination also applies to gender identity, since discrimination based on gender identity — and against trans people — is fundamentally rooted in expectations of what people of certain sexes assigned at birth should be like.

So the Obama administration sent out guidance to public schools making this more formal policy, establishing policies that schools should try to follow. But until courts validate the guidance, it’s really a legally non-binding set of guidelines.

Yet if courts approve of the Obama administration’s interpretation of federal civil rights law, it could effectively expand existing civil rights protections that explicitly ban discrimination based on race and sex, among other traits, to explicitly include gender identity. And that could, in turn, bleed over to federal civil rights laws beyond Title IX and education — such as the Civil Rights Act’s protections in the workplace and the Fair Housing Act’s provisions for housing. (A case dealing with these issues is in front of the Supreme Court right now.)

The trans-friendly interpretation of federal civil rights law, however, has run into a big political hurdle: bathrooms. Under the trans-friendly interpretation of the law, school officials are discriminating — and violating civil rights law — if trans students are blocked from using a bathroom or locker room for their gender identity. After all, forcing trans people to use the facility that doesn’t align with their gender identity acts as a reminder that society still isn’t completely willing to accept them and their identities, even if trans people pose no danger to anyone else.

This has become a major flashpoint in the LGBTQ rights debate — taking off last year when North Carolina passed HB2, which prohibits trans people in the state from using the bathrooms and locker rooms that align with their gender identity in schools and government buildings. When the Obama administration sued North Carolina and sent out its guidance to schools across the country, the bathroom issue became an even bigger deal — even though the anti-trans talking point that sparked it is based on a huge myth.

The counterargument to the guidance is based on a myth about trans people and bathrooms

Underlying this entire issue is a big myth about trans people, nondiscrimination laws, and bathrooms.

According to supporters of North Carolina’s HB2 and other opponents of the Obama administration’s guidance, letting trans people use the bathroom for their gender identity would pose a public safety risk. They claim that if trans people can use the bathroom that aligns with their gender identity, men will take advantage of such policies to disguise themselves as trans women and sneak into women’s bathrooms or locker rooms to sexually assault or harass women.

Some religious conservatives have latched onto this myth to oppose laws that ban discrimination against sexual orientation and gender identity in the workplace, housing, public accommodations, and education — particularly after a big win in Houston, where voters struck down a local nondiscrimination law after opponents of the ordinance trumpeted the bathroom myth. North Carolina's law, for instance, came after Charlotte added sexual orientation and gender identity to its nondiscrimination protections for public accommodations. (More on all of that history in Vox's broader explainer.)

This is the argument that Texas has repeatedly cited to defend its position before and after it filed a lawsuit, with several other states, against the Obama administration’s guidance.

But even if trans people are allowed to use the bathroom for their gender identity, sexual assault remains illegal. So a legal deterrent to deviant behavior already exists.

There's also no evidence that nondiscrimination laws — and other policies that also let trans people use the bathroom for their gender identity — lead to sexual assault in bathrooms and locker rooms. In two investigations, Media Matters confirmed with experts and officials in 12 states and 17 school districts with protections for trans people that they had no increases in sex crimes after they enacted their policies.

Conservatives usually counter that there are examples of men sneaking into women's bathrooms to attack women. But as PolitiFact reported, none of the examples cited in the US happened after a city or state passed a nondiscrimination law or otherwise let trans people use the bathroom or locker room for their gender identity. Instead, these seem to be examples of men doing awful things regardless of the law — which has, unfortunately, happened since the beginning of civilization.

One example is a case in Toronto, Canada, which now has a nondiscrimination law, in which a man disguised himself as a woman and attacked women in shelters. But the attacks happened months before Ontario (Toronto's province) protected trans people in a nondiscrimination law. So the law couldn't have been the cause.

Still, the myth has persisted, trickling up in some way or another all the way to legal battles over federal laws. And it’s a big reason the Trump administration is now poised to stop defending trans students’ civil rights — and why LGBTQ groups are so worried.