Already faced with the threat of impending legal challenges, supporters of Illinois’ new “assault weapon” ban face a new obstacle: mass non-compliance.

Following last week’s passage of a ban on so-called assault weapons and high-capacity magazines, the Sheriffs of more than 80 Illinois counties have released statements calling the law “unconstitutional.” They have publicly declared their refusal to enforce it in most circumstances. The total number who voiced their intention of disregarding the law represent nine in 10 of the state’s sheriffs, according to the Associated Press.

“I, among many others, believe HB 5471 is a clear violation of the 2^nd Amendment to the U.S. Constitution,” DuPage County Sheriff James Mendrick, whose jurisdiction is the second most populous in the state, said in a public letter. “Therefore, as the custodian of the jail and the chief law enforcement official for DuPage County, neither myself nor my office will be checking to ensure that lawful gun owners register their weapons with the state, nor will we be arresting or housing law-abiding individuals that have been arrested solely with non-compliance of this Act.”

The backlash among key law enforcement figures across the state significantly hinders the efforts of gun-control advocates and the state’s Democratic lawmakers. With just one day left in the state’s lame-duck legislative session, party leadership was able to shepherd a statewide assault weapon ban through the legislature after decades of failed efforts. Now, with the prospect of legal challenges hanging over their heads and the mass non-compliance of broad swaths of the state all but guaranteed, those efforts could end up being in vain.

Illinois Governor J.B. Pritzker (D.), who made an assault weapon ban a crucial promise of his reelection, expressed outrage over the county sheriffs’ defiance against the new law.

“This is political grandstanding at its worst,” he told Fox News. “Sheriffs have a constitutional duty to uphold the laws of the state, not pick and choose which laws they support and when. Anyone who advocates for law, order, and public safety and then refuses to follow the law is in violation of their oath of office.”

Several Democratic state lawmakers also spoke out against the Sheriffs’ statements, including those representing districts with dissenting law enforcement officials.

“The sheriff has no authority to determine the constitutionality of a law — that is up to the courts,” a statement signed by 16 state legislators representing districts within DuPage County reads. “Nor can he pick and choose which laws to enforce; he must enforce them all.”

The new law, which took effect last Tuesday, outlaws the sale and manufacture of more than 170 semi-automatic rifles, pistols, and shotguns by make and model. Possession of the banned weapons will also be prohibited within 300 days unless a person lawfully acquired the firearm before the ban and registered it with the Illinois State Police. Furthermore, the law bans the sale and manufacture of handgun magazines capable of holding more than 15 rounds of ammunition, long gun magazines capable of holding more than ten rounds of ammunition, .50 caliber firearms and ammunition, and expands the duration of the state’s “red flag” restraining order from six months to one year.

Many law enforcement officials, including the Illinois Sheriffs Association, opposed the measure while it was being considered in the legislature. The association released the model statement that began circulating among Sheriffs announcing their refusal to enforce the ban.

The law is also expected to draw several lawsuits from gun-rights groups. The Illinois State Rifle Association previously told The Reload it was working with the Second Amendment Foundation and Firearms Policy Coalition on an imminent court challenge.