Lawyers for Oregon standoff leader Ammon Bundy have argued that federal officials lack authority to prosecute the anti-government protesters in a new court motion that offers a glimpse of the constitutional debate activists hope to bring to a high-profile trial.

Bundy, who led an armed occupation of the Malheur national wildlife refuge, has long claimed that the federal government has no right regulating public lands in the west, and now his legal team is bringing that argument directly to US prosecutors, who have filed a slew of serious felony charges against the activist.

The new motion, which lays the groundwork for a request to dismiss the criminal case against Bundy, presents an argument that legal experts have rejected as an inaccurate interpretation of the US constitution – that the federal government has unlawfully claimed ownership over the wildlife refuge and other public lands.

“The purposes intended for the federal government, were, among other things, defense, trade, and to settle disputes between States,” wrote Lissa Casey, one of Bundy’s lawyers. “Defendant will argue that the Constitution only intended to give broad federal power of property in Territories, as the Founders contemplated the expansion westward.”

The “land that is now the Malheur National Wildlife Refuge was not always ‘federal land’. The federal government relinquished that land when it was previously deeded and homesteaded”, Casey’s filing continued.

Duane Ehmer rides his horse Hellboy at the occupied Malheur National Wildlife Refuge in Burns, Oregon on 7 January 2016. Photograph: Rob Kerr/AFP/Getty Images

This argument has gained significant traction in recent years within a growing anti-government land-use movement in the west, spearheaded by Ammon’s father Cliven Bundy, the Nevada rancher who long refused to pay grazing fees to allow his cattle to use public lands and led an infamous 2014 standoff at his property.

The Bundys and their supporters have repeatedly claimed that Article 1, Section 8, Clause 17 of the constitution restricts federal ownership of land in such a way that national parks, monuments and federally protected wildlife and wilderness areas are unconstitutional. Constitutional experts say they are misreading a narrow clause and that it is well established that the federal government has broad authority to manage public lands.

Ammon, 40, led the Oregon occupation in January to protest the government’s treatment of local ranchers in a standoff that dragged on for 41 days and resulted in the arrest and charging of more than two dozen activists.

The protesters are accused of using “force, intimidation and threats” to conspire against the government along with a number of firearm charges that could lead some of them to spend decades behind bars if they are convicted and sentenced with maximum punishments.

After his arrest, Ammon told supporters that they planned to bring the constitutional fight against federal land control from the refuge to the courts – and his attorneys say the new motion is a key step in advancing the cause.

“These protesters are in it for the long haul,” Mike Arnold, another attorney for Ammon, said in an interview Monday. “Phase one was the protest. Phase two is taking the case to the courts. They are running to this fight, not away from it.”

Arnold said that Ammon “respects the authority of the federal government”, but argued that he has a right to challenge past constitutional interpretations and case law that have confirmed federal authority of lands.

“You can disagree with their methods and tactics and interpretation. But you cannot deny that they brought attention to the actual words of the constitution,” Arnold added.

Arnold argued that the Oregon protest was an act of “civil disobedience” and that even if the motion to dismiss based on lack of federal jurisdiction fails, he expects Ammon to be found not guilty at trial, which is scheduled to begin in September.

Prosecutors have argued that Ammon and his followers led a coordinated and violent takeover of government buildings and have cited social media posts as evidence.

The US district attorney’s office has not yet responded to the defense’s new motion, and a spokesperson did not immediately respond to request for comment.