Bump stock owner Damien Guedes and three pro-gun groups – Firearms Policy Coalition (FPC), Firearms Policy Foundation (FPC) and the Madison Society Foundation (MSF) – filed a lawsuit against the Department of Alcohol, Tobacco, Firearms and Explosives (ATF). They are seeking a preliminary injunction, which would keep the ATF from enacting the new bump stock regulation while the court's review its constitutionality.

The plaintiffs argue that the Trump administration's definition of a "bump stock" and a "machine gun" are not one and the same. They're also challenging Acting Attorney General Matthew Whitaker's authority to issue regulations without being nominated to the role and confirmed by the Senate or by operation of law.

From the lawsuit:

Ignoring the will of Congress by subverting the Attorney General Succession Act (“AGSA”), 28 U.S.C. § 508, President Donald J. Trump unlawfully appointed Matthew Whitaker as Acting Attorney General, in spite of clear statutory direction that Rod J. Rosenstein as Deputy Attorney General was to assume the duties and responsibilities of Attorney General. As such, Final Rule promulgated and executed by Matthew Whitaker on December 18, 2018 is unlawful and invalid. Further, despite Congress expressly defining the term “machinegun” in the Gun Control Act, 18 U.S.C. § 921, et seq. (“GCA”) and the National Firearms Act, 26 U.S.C. § 5801, et seq. (“NFA”), along with ATF’s prior acknowledgement that a bump stock was not a “machinegun” nor subject to regulation under the GCA and NFA, Defendants have implemented a final rule in an arbitrary and capricious manner which denies Plaintiffs, and those similarly situated, the ability to retain a bump stock, despite reliance on prior determinations made by the Bureau of Alcohol, Tobacco, Firearms and Explosives (“ATF”). Accordingly, a preliminary injunction is warranted and necessary to prevent ATF from enforcing this new rule during the pendency of this litigation.

Under the regulation, bump stock owners have until March 21st to turn in their accessory. If they don't, "they could face federal ‘machinegun’ charges that carry up to 10 years in prison and $250,000 in fines for each violation," the groups said in a statement.

According to Joshua Prince, one of the attorneys representing the plaintiffs, the ATF lied to gun owners.

“The ATF has misled the public about bump-stock devices. Worse, they are actively attempting to make felons out of people who relied on their legal opinions to lawfully acquire and possess devices the government unilaterally, unconstitutionally, and improperly decided to reclassify as ‘machineguns,'" Prince said. "We are optimistic that the court will act swiftly to protect the rights and property of Americans who own these devices, and once the matter has been fully briefed and considered by the court, that the regulation will be struck down permanently.”

Gun Owners of America vowed to file a similar lawsuit for an injunction.

Here's the full lawsuit: