Assault-rifle owners statewide are organizing a mass boycott of Gov. Cuomo’s new law mandating they register their weapons, daring officials to “come and take it away,” The Post has learned.

Gun-range owners and gun-rights advocates are encouraging hundreds of thousands of owners to defy the law, saying it’d be the largest act of civil disobedience in state history.

“I’ve heard from hundreds of people that they’re prepared to defy the law, and that number will be magnified by the thousands, by the tens of thousands, when the registration deadline comes,’’ said Brian Olesen, president of the American Shooters Supply, one of the largest gun dealers in the state.

Officials estimate at least 1 million semiautomatic rifles are owned in the state, sources said.

And come April 15, 2014 — when Cuomo is expected to be running for re-election — they all have to be registered with the State Police.

But because the rifles have been legal but unregistered until now, authorities don’t know who has them or where they are located.

State officials will be nervously watching the registration figures to see how many gun owners comply, sources said.

“I believe you will have people stepping forward, saying, ‘Here I am. See? I have what you call an assault rifle. Now come and take it away,’ ’’ said a gun-rights activist and boycott organizer.

That’s exactly what state officials are worried about.

“Many of these assault-rifle owners aren’t going to register; we realize that,’’ said a Cuomo-administration source who added that officials expect “widespread violations’’ of the new law. Owners who refuse to register could face a class-A misdemeanor — punishable by up to a year in prison.

And an owner’s weapon could also be confiscated, which could be worth several thousands of dollars.

National Rifle Association President David Keene told The Post yesterday that he wasn’t surprised by the planned boycott.

“While we don’t get involved in campaigns to resist the law, I will say this: Historic experience here and in Canada shows that when you try to force gun owners into a registration and licensing system, there’s usually mass opposition and mass noncompliance,” he said. “I think it’s going to be very difficult for the governor to get mass compliance with this new law.”

Leaders of some of the state’s 300 gun clubs, gun dealers and Second Amendment organizations are organizing the boycott — and the heaviest interest is in Suffolk County, the Capital District and the Buffalo region, sources said.

The organizers point to a little-known guarantee of gun ownership contained in New York’s own “Civil Rights Law,” which was ratified the same year as the Constitution .

The state statute says the right to keep and bear arms “cannot be infringed” — stronger than the Second Amendment, which says it “shall not be infringed.’’

“They’re saying, ‘F— the governor! F— Cuomo! We’re not going to register our guns,’ and I think they’re serious. People are not going to do it. People are going to resist,’’ said State Rifle and Pistol Association President Tom King, a member of the NRA board of directors. “They’re taking one of our guaranteed civil rights, and they’re taking it away.’’

Olesen said he’ll soon launch a nonprofit, to be called Save the Second Amendment Foundation,’ to fight the new law.