Why is the Democratic frontrunner taking issue with the law? The controversial measure, which was passed during the administration of President George W. Bush, effectively shields gun manufacturers from all liability for the harm caused by people who criminally or unlawfully misuse their products. And opponents of the law say that that immunity creates a disincentive for gun safety, especially at the point of sale, and keeps consumers from filing lawsuits that could result in improved gun safety.

In outlining her gun control agenda, Clinton called the law dangerous. “It is past time to repeal this law and hold the gun industry accountable just like everyone else.”

When President Bush signed the act into law in 2005, gun manufacturers were in attendance. The National Rifle Association had lobbied heavily for its passage, arguing that the law would prevent lawsuits that could harm the firearm industry and infringe on Americans’ right to bear arms. At the time, longtime NRA leader Wayne LaPierre called the measure “the most significant piece of pro-gun legislation in 20 years,” adding that “history will show that this law helped save the American firearms industry from collapse under the burden of these ruinous and politically motivated lawsuits.”

The law was introduced during an onslaught of litigation by city governments, which sought to hold gun companies responsible for creating a “public nuisance” by supplying the public with weapons.

But since its passage, the law has served as a powerful legal defense against a different type of lawsuit: those filed by gun violence victims and their families against gun manufacturers for not equipping their weapons with adequate safeguards and against gun dealers for selling guns improperly.

In 2009, for instance, the Illinois Supreme Court rejected a case brought by the family of a child killed by a 13-year-old friend, who was playing with his father’s loaded pistol. The family said the gun design was flawed, but the state court ruled that the company was shielded by the Protection of Lawful Commerce in Arms Act.

Following the 2012 Aurora, Colo. movie theatre shooting, Marc Bern, a lawyer for the victims’ families, told The Washington Post that the law limited his clients’ options. They sued the movie theatre company but not the companies that supplied the gunman’s firearms and ammunition because of their ability to “insulate” themselves with the Lawful Commerce law.

The immunity that the gun industry receives by way of the law is nearly unprecedented. (Vaccine makers are another group that have some immunity from lawsuits brought by injured patients.)

Opponents of the law argue that such protection not only prevents families of gun violence victims from seeking justice, but that it also stymies lawsuits that could push for changes to gun designs and sales procedures that could make people safer. There’s precedent for this argument: Decades of lawsuits against automakers forced car manufacturers to install seat belts and airbags.

Like any gun control effort, a repeal of the Protection of Lawful Commerce in Arms Act, will face resistance from the NRA and forces within Clinton’s own party. The Obama administration has filed legal briefs supporting the constitutionality of the legal shield, citing the Interstate Commerce Clause.