Two Massachusetts lawmakers, Sen. Edward Markey and Rep. Joe Kennedy, introduced legislation in both Congressional houses that would prohibit trans and gay panic defences throughout the United States.

A ‘gay panic’ defence claims that individuals are not in control of their violent acts due to the psychological panic they experience when in contact with LGBT+ people. Although the defence tactic is usually unsuccessful, it allows states to endorse homophobic and transphobic bias. “Murdering or assaulting anyone because of their sexual orientation or gender identity is not a defence, it is a hate crime,” Kennedy, who chairs the Congressional transgender equality task force, said in a statement announcing the proposed bill. “Legal loopholes written into our laws that seek to justify violent attacks against our gay, lesbian, bisexual, and transgender neighbours should never have existed in the first place.”

The murder of Matthew Shepard in 1998 is one of the most well-known cases that used the gay panic defence. Shepard was a gay student at the University of Wyoming. He was attacked, beaten and tortured while tied to a fence where he was left to die. One of the two perpetrators claimed that he acted violently after Shepard allegedly touched his knee.

Jason Marsden, the executive director of the Matthew Shepard Foundation, told ABC News that the proposed legislation is “particularly timely.” “There’s an astonishing number of homicides and other attacks on trans persons,” Marsden said, “and we’re starting to see a trans panic defence trotted out in a number of cases.”

Such as the death of Islan Nettles in 2013. Nettles was beaten to death in Harlem, New York City. The killer, James Dixon, turned himself in three days after the attack stating that he was in “a blind fury” after discovering Nettles was a transgender woman. Despite the confession, Dixon wasn’t indicted until March 2015. He revealed that his friends had mocked him for flirting with Nettles without realizing her gender identity. Dixon was not charged with murder nor a hate crime.

Jenny Pizer, the law and policy director of LGBT+ advocacy group Lambda Legal stated that panic defences are based on “the idea that violent vicious reactions to LGBT people are understandable because there’s something about us that is so shocking and so horrifying that a violent reaction is to be understood.”

The use of trans and gay panic defences is currently legal in 47 states with California, Illinois and Rhode Island the only states to have passed laws banning its use. Eight other states have introduced legislation to ban. If the proposed legislation passes, it will not apply in state-level criminal cases. Advocates are hopeful that the federal law would influence states to pass their own anti-panic laws.

“Historically we have seen panic defences used as a Trojan horse to attempt to bring societal prejudices and hatred against LGBTQ people, and especially transgender women and gay men, into courtrooms in an effort to justify types of violence that are simply never justifiable,” Sue Yacka-Bible, communications director at GLAAD, told ABC News in a statement.

Yacka-Bible continued, “Explicitly banning this practice will go a long way in protecting survivors and the friends and family of victims, as they engage with the criminal legal system at a deeply painful period of their lives.”