The Trump administration is reportedly considering a rule change that would define “sex” to mean a person's biological gender at birth.

According to The New York Times, which broke the story, the proposed change would define sex as either male or female – an immutable characteristic defined at birth by a person's genitals. Genetic testing would be required to challenge a person's own sex.

The Times wrote that the proposal would amount to “defining transgender out of existence.”

The Human Rights Campaign (HRC), the nation's largest LGBT rights advocate, responded by calling on Congress to approve the Equality Act, a bill that seeks to prohibit discrimination based on sexual orientation and gender identity.

(Related: Nancy Pelosi promises top priority for LGBT Equality Act, if Democrats retake House.)

“Defining ‘sex’ in this narrow language tailored to the talking points of anti-equality extremists is part of a deliberate strategy to eliminate federal protections for LGBTQ people,” HRC President Chad Griffin said in a statement. “This is a direct attack on the fundamental equality of LGBTQ people and, if this administration refuses to reverse course, Congress must immediately take action by advancing the Equality Act to ensure that LGBTQ people are explicitly protected by our nation’s civil rights laws.”

The move is the latest salvo in an ongoing war against the transgender community. The Trump administration is currently seeking to ban transgender troops and has reversed Obama-era guidance on allowing transgender students attending public schools to use the bathroom of their choice. The Department of Justice has argued that federal laws prohibiting sex discrimination in the workplace do not apply to people who are LGBT.

The American Civil Liberties Union (ACLU) called the reported roll-back an “attack on the very lives and existence of transgender people” and vowed to challenge the administration in court.

“If the Trump administration moves forward with these hateful and hurtful policies, they will once again be met with opposition in courts and in communities,” the ACLU said in a statement. “More and more courts are seeing that policies targeting transgender people have no place in our country.”