TOPEKA, Kan. (AP) – 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.