? U.S. Attorney General Eric Holder told Gov. Sam Brownback that a new Kansas law that criminalizes federal enforcement of gun laws was unconstitutional.

Holder also warned that the federal government “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.”

The dispute is over Senate Bill 102, which Brownback signed into law last month. The Second Amendment Protection Act excludes from federal regulation any gun made or owned in Kansas. It will allow law enforcement in Kansas to charge and convict federal authorities with crimes if they try to enforce action against a Kansas-protected gun.

Holder said in a letter to Brownback, “In purporting to override federal law and to criminalize the official acts of federal officers S.B. 102 directly conflicts with federal law and is therefore unconstitutional.” Holder said the Bureau of Alcohol, Tobacco, Firearms and Explosives, the FBI, the Drug Enforcement Administration and U.S. Attorney’s Office for the District of Kansas would continue to enforce federal firearms laws and regulations.

Brownback signed the bill on April 16. The law became effective April 25, and Holder sent the letter one day later.

Supporters of the bill, including the Kansas State Rifle Association, said it was necessary in light of attempts by the federal government to adopt new gun restrictions and regulations.

Kansas Secretary of State Kris Kobach who was one of the co-authors of the law defended it, saying the law will withstand any legal challenge.

“With respect to any litigation, we will happily meet Mr. Holder in court,” Kobach said.

Since the law governs guns that remain in Kansas, they are exempt from the interstate commerce power of the federal government, he said.

“While some federal regulations of firearms are permissible exercises of the interstate commerce power, others clearly are not. One of the things that the federal government cannot do is regulate firearms that have never travelled in interstate commerce and that have no substantial effect on interstate commerce — firearms covered by SB 102,” Kobach said.

But U.S. Attorney Barry Grissom issued a statement calling the state law, “illegal, unenforceable, and also bad policy.”

Grissom said the statute threatens federal officers who are trying to keep the keep the United States safe. “These hard-working federal employees cannot be forced to choose between the risk of a criminal prosecution and the continued performance of their federal duties,” he said.

Kansas Attorney General Derek Schmidt has said it would cost $625,000 to defend legal challenges against the law, according to a memo from the Kansas Legislative Research Department.

The bill was approved by wide margins in the Legislature: 35-4 in the Senate and 96-24 in the House. Among Douglas County legislators, only state Sen. Marci Francisco, D-Lawrence, and state Rep. John Wilson, D-Lawrence, voted against the final bill.

Meanwhile, Kansans continue to apply for concealed-carry permits in huge numbers.

The state attorney general’s office received 3,462 applications for permits in April, which was slightly down after three consecutive record-breaking months.

A year before, the state processed 1,442 applications in the month of April. In the past four months, 14,274 Kansans filed new concealed-carry applications. There are now 55,988 active concealed-carry licensees in Kansas.