U.S. Attorney General Eric Holder has told Kansas Gov. Sam Brownback that a new state law attempting to block federal regulation of some guns is unconstitutional and that the federal government is willing to go to court over the issue.
The U.S. attorney's office for Kansas on Thursday released a copy of a letter from Holder to Brownback.
The letter is dated April 26, the day after Kansas' law took effect.
Kansas' law declares that the federal government has no authority to regulate guns, ammunition and accessories manufactured, sold and kept only in Kansas. The law also makes it a felony for a federal agent to enforce any law, regulation, order or treaty covering those items.
The new statute says that Kansas-only guns, ammunition and accessories aren't a part of interstate commerce, which the federal government regulates under the U.S. Constitution.
But Holder said in his letter that the Constitution prohibits states from pre-empting federal laws.
"Kansas may not prevent federal employees and officials from carrying out their official responsibilities," Holder wrote in his letter. "And a state certainly may not criminalize the exercise of federal responsibilities."
Aides to Brownback and Kansas Attorney General Derek Schmidt did not immediately return telephone and email messages seeking comment.
The Kansas law is modeled on a 2009 Montana law that is being reviewed by a federal appeals court, and Missouri and Oklahoma lawmakers are considering similar legislation.
Supporters of the Kansas law softened it - to say that federal agents wouldn't be arrested or detained while trials were pending - and insist that it will withstand court scrutiny.
But Schmidt's office has already anticipated a potential legal challenge from the federal government, and has asked legislators to increase its budget by $225,000 over the next two years to cover litigation costs.
Gun-rights supporters in Kansas made an urgent push for the law this session, as President Barack Obama, some members of Congress and other officials discussed gun control proposals in the wake of the December massacre at a Newtown, Conn., elementary school.
Supporters have said they worry about attempts by the federal government to restrict or ban the sale of some weapons - or even confiscate them.
Holder said in his letter that federal law enforcement agencies will "continue to execute their duties to enforce all federal firearms laws and regulations."
"Moreover, the United States will take all appropriate action, including litigation if necessary, to prevent the State of Kansas from interfering with the activities of federal officials enforcing federal law," Holder wrote.