Arizona Republicans are rallying behind a proposed law that critics say would amount to legalizing murder.

House Bill 2843 would expand the “Castle Doctrine,” which gives people the right to use deadly force when threatened by home intruders, to include trespassers. State Rep. Justin Heap (R) filed the bill to give people living in the border state wider latitude to use force against unauthorized migrants who cut through private property on their way into the United States.

“It’s horrifying that Republicans want to allow people to legally shoot and kill migrants,” state Rep. Analise Ortiz (D) told HuffPost. “Especially when so many folks are seeking their legal right to seek asylum in the United States. It’s just wrong.”

The bill stems from a decadeslong trend in conservative state legislatures to expand the right of individuals to protect themselves with firearms. Such “stand your ground” laws typically remove the obligation for people to retreat to safety when they feel threatened, and extend immunity to prosecution for those who commit a homicide in cases where they believe they face an attack.

Heap said at a Judiciary Committee hearing last month that he filed the bill over concerns brought by local prosecutors who were “having issues in the case where you have farmers and ranchers who want to trespass someone from their property,” by which he meant “remove someone from their property.” He noted concerns about migrants and human traffickers specifically.

But Heap’s proposal is more unique than that description suggests, according to Lindsay Nichols, policy director for the Giffords Law Center to Prevent Gun Violence. Castle Doctrine laws, including Arizona’s, have not historically applied to areas outside a person’s home.

“It’s a particularly alarming instance of this trend,” Nichols said. “The prospect of a world in which you can be executed without due process for accidentally stepping onto someone’s property is terrifying.”

Dustin Williamson, the regional legal director at Everytown for Gun Safety, said Arizona’s expansive gun laws would make the proposal even more dangerous.

“Arizona already has a dangerous Shoot First law on the books that allows people to shoot and kill others even if they know they can easily and safely walk away from a confrontation,” Williamson wrote in an email. “To prevent senseless acts of gun violence, lawmakers in the state should reject any attempt to broaden its self-defense laws to further encourage armed vigilantism.”

The Arizona House of Representatives passed the bill last week on partisan lines and it has favorable odds in the Senate. Republicans control both houses of the Arizona legislature with slim majorities.

The bill is unlikely to become law. Observers expect the state’s Democratic governor, Katie Hobbs, to veto the bill if both bodies pass it. Hobbs’ office did not respond to a request for comment.

Still, opponents say the proposal harnesses hostility over the hot-button issue of immigration to legalize activity that today constitutes murder.

The real-life example of rancher George Alan Kelly is playing out in state court as Heap’s bill moves through the legislature. Heap did not cite the case specifically when explaining his proposal, but Kelly has made headlines for allegedly shooting into a group of unauthorized migrants traveling across his ranch.

Prosecutors portray Kelly’s case as far from one of self-defense, however. Kelly, 75, has contended that a man within a group of migrants traveling along his property wielded a semi-automatic rifle. But the criminal complaint against Kelly says that no one within the group possessed a weapon and that Kelly fired without warning from a hidden position.

Kelly changed his story about why he opened fire several times. He told sheriff’s deputies that he did not know how Gabriel Cuen Butimea, 48, died and had backed away from the body when he found it, according to court records.

Upon arriving at the location of Cuen Butimea’s corpse, however, Kelly commented that the man died from a shot through the lung and heart. Law enforcement officials could only confirm the exit wound by repositioning the body, court records say.

Kelly later admitted to opening fire at the group of migrants, but said he only fired warning shots. He is scheduled to face trial for second-degree murder and aggravated assault this month.