Governor Jay Nixon has vetoed legislation that would have made it a crime for federal agents to try to enforce federal gun control laws in Missouri.
Nixon said the U.S. Constitution generally gives supremacy to federal laws over conflicting state ones.
The bill would have made it a misdemeanor crime for federal agents to attempt to enforce any federal gun regulations that "infringe on the people's right to keep and bear arms."
It also sought to invalidate some specific federal laws, including a 1934 law that imposed on tax on transferring machine guns or silencers.
And under the bill, journalists could have faced charges for publishing the names of gun owners.
Nixon said that would have violated free speech rights.
In a news release, the Governor said "As a gun owner and hunter, I support 2nd amendment rights of Missourians and oppose efforts to undermine them."
Nixon said that's why he signed Callaway County Representative Jeanie Riddle's bill to allow state workers to have guns in their vehicles while parked on state property.
That bill also allows fire chiefs with concealed-gun permits and special approval to carry weapons on the job.
And it bars governments from running gun-buyback programs unless those guns are later offered for sale or trade to licensed firearm dealers.
Missouri House Speaker Tim Jones said he wants to try to override Nixon's veto of the federal gun law ban.
The republican told the Associated Press he is "shocked and astounded" by Nixon's veto.
He believes "a supermajority of Missourians" want lawmakers to override the veto.
An override would require a two-thirds vote in both the House and Senate during a September session.
Republicans have the numbers in both chambers of the legislature to do that without any Democratic support.
In other action, Nixon signed legislation that reinstates local taxes on vehicles bought from out-of-state dealers, or through person-to-person sales.
That follows two earlier vetoes of similiar bills.
The Missouri Supreme Court last year said cities and counties could charge so-called "use taxes" on such vehicles only if approved by local voters.
The new state law redefines vehicle sales taxes by applying them to the titling, not the purchase of vehicles.
It then requires some local governments to hold public elections on whether to keep or repeal the redefined vehicle tax.