The Trump administration on Tuesday issued a final rule that bans so-called bump stocks, devices that allow semiautomatic weapons to fire more rapidly, saying tens of thousands of them around the country must be destroyed or surrendered to federal law enforcement.

The rule could now tee up a possible lawsuit challenging the ban.

The rule will take effect after 90 days, a senior Justice Department officials told reporters, explaining, “At that point, it will be illegal to have a bump stock–type device. They will be considered a machine gun.”

“We expect most owners will comply with the law and follow instructions or hand them in to ATF," the official added. "As with any law, we rely on lawful compliance.”

After an October 2017 massacre in Las Vegas in which a gunman fired on a crowd using a bump stock attached to a rifle, President Donald Trump suggested the devices should be prohibited. The Justice Department received more than 186,000 comments on a proposal released this spring, leading to the 157-page final rule released Tuesday.

“Specifically, these devices convert an otherwise semiautomatic firearm into a machine gun by functioning as a self-acting or self-regulating mechanism that harnesses the recoil energy of the semiautomatic firearm in a manner that allows the trigger to reset and continue firing without additional physical manipulation of the trigger by the shooter,” says the final rule, which hews closely to language proposed in March.

“Hence,” it continues, “a semiautomatic firearm to which a bump-stock-type device is attached is able to produce automatic fire with a single pull of the trigger.”

That conclusion contradicts the position previously held by both the Obama and Trump administrations, which had deemed the attachments don’t make firearms fully automatic.

Officials at the Bureau of Alcohol, Tobacco, Firearms and Explosives — a division of the Justice Department known as ATF — previously found that, since pressure must be applied to the gun from behind in addition to pulling the trigger, the devices evade a ban on machine guns under the National Firearms Act and Gun Control Act.

In a letter dated April 6, 2017, to a bump stock manufacturer, Michael Curtis, chief of the Firearms Technology Industry Services branch of the ATF, said its product was not prohibited. “Since your device does not initiate an automatic firing cycle by a single function of the trigger, FTIB finds it is NOT a machinegun under the NFA, 26 U.S.C. § 5845(b) or the amended GCA, 18 U.S.C. § 921(a)(23),” Curtis wrote.

The about-face from the Trump administration has led to widespread speculation of a lawsuit that would challenge the new rule by arguing it’s an incorrect reading of the law.

“We will be ready to defend not matter who files” a lawsuit, the Justice Department official said Tuesday, adding that the government reached a new interpretation of the older laws, passed when machine guns were made of metal, considering bump stocks are fashioned from plastic. “After the Las Vegas shooting, we took another look.”

Still, it remains unclear how the devices have changed since the Trump administration determined in April 2017 that bump stocks could not be banned under existing law.

The device has brought intense attention since the mass shooting in Las Vegas last year. In the aftermath of that shooting, even the National Rifle Association said lawmakers should review the devices to see if they “comply with federal law.”