WICHITA, Kan. (AP) — When Shane Cox began selling his homemade firearms and silencers out of his military surplus store, he stamped “Made in Kansas” on them to assure buyers that a Kansas law would prevent federal prosecution of anyone owning firearms made, sold and kept in the state.

The 45-year-old Chanute resident also handed out copies to customers of the Second Amendment Protection Act passed in 2013 by the Kansas Legislature and signed by Gov. Sam Brownback, and even collected sales taxes. His biggest selling item was unregistered gun silencers that were flying out of the shop as fast as Cox could make them, prosecutors said later. One of those customers — 28-year-old Jeremy Kettler of Chanute — was so enthusiastic about the silencer that he posted a video on Facebook.

But last week, a jury found Cox guilty of violating federal law for the manufacture, sale and possession of unregistered firearms and silencers. Kettler was found guilty on one count for possessing the unregistered silencer.

The case could reverberate across the country because it cites the Second Amendment to the U.S. Constitution, pitting the federal government’s right to regulate firearms against the rights of states. The judge overseeing the case expects it ultimately to end up before the U.S. Supreme Court.

At trial, defense attorneys contended their clients believed the Kansas law made their activities legal, arguing they are “caught in the crossfire” of the struggle between the state and the federal government over gun control.

Cox and Kettler were convicted under the National Firearms Act, which is a part of the Internal Revenue code enacted under Congress’ power to levy taxes. The case raises the question of whether that taxing authority can be used to regulate firearms that stay within state borders. Advocates for state’s rights also contend such guns do not fall under Congress’ power to regulate interstate commerce.

Kettler told jurors he bought the unregistered silencer “because of a piece of paper signed by the governor saying it was legal.” Before trial, he criticized Kansas for “setting up its citizens to be prosecuted” by the federal government.

Jim Howell, a former Republican state representative, said he physically carried the bill around the Capitol and got 55 legislators to co-sponsor the legislation, which won bipartisan support. Lawmakers knew when they passed the law that there was going to be disagreement on who has authority to regulate firearms if they stay inside the state of Kansas, he said.

“I think these gentlemen understood that when they made a choice to do what they did,” Howell said.

Kansas Attorney General Derek Schmidt has intervened to defend the state law’s constitutionality in the first criminal case that has used the Kansas law as a defense. Schmidt said in a statement that buyers’ reliance on the state law as a defense is “reasonable, and it is consistent with the State’s interest in ensuring the Second Amendment Protection Act itself is defended.”

That state law says firearms, accessories and ammunition manufactured and kept in Kansas are exempt from federal gun control laws. It also made it a felony for the federal government to enforce them.

A day after it took effect, then-U.S. Attorney General Eric Holder advised Brownback that the state law criminalizing federal enforcement of gun laws was unconstitutional.

The Brady Campaign to Prevent Gun Violence challenged its legality in a 2014 civil lawsuit that was thrown out because a judge deemed the group did not have standing to sue.

Kansas modeled its law on the Montana Firearms Freedom Act, which the Court of Appeals for the Ninth Circuit has found to be invalid, according to court filings.

State firearm nullification laws, or firearms freedom acts as they are sometimes called, have been signed into law in nine states. In addition to Montana and Kansas, other states with them include Alaska, Arizona, Idaho, South Dakota, Tennessee, Utah and Wyoming, according to Everytown For Gun Safety, which advocates common-sense gun control laws.

The legal maneuvering comes against the backdrop of President-elect Donald Trump’s election following a campaign that made gun rights a rallying cry for his supporters. A new U.S. attorney general will also be in place at the Justice Department.

And in another twist, the man who helped write the state’s gun law — Kansas Secretary of State Kris Kobach — is now a potential pick for a job in the Trump administration. Kobach has called this case “a perfect example of a prosecution that should never occur.”

Sentencing is set for Feb. 6.