JEFFERSON CITY, Mo. (AP) — In the nation's agricultural heartland, farming is more than a multibillion-dollar industry that feeds the world. It could be on track to become a right, written into law alongside the freedom of speech and religion.

Some powerful agriculture interests want to declare farming a right at the state level as part of a wider campaign to fortify the ag industry against crusades by animal-welfare activists and opponents of genetically modified crops.

The emerging battle could have lasting repercussions for the nation's food supply and for the millions of people worldwide who depend on U.S. agricultural exports. It's also possible that the right-to-farm idea could sputter as a merely symbolic gesture that carries little practical effect beyond driving up voter turnout in local elections.

"A couple of years from now, we might say this was the beginning of the trend," said Rusty Rumley, a senior staff attorney at the National Agricultural Law Center in Fayetteville, Arkansas. But "we really don't even know what they're going to mean."

Animal advocates and other groups are increasingly urging consumers, grocers and restaurants to pay as much attention to how their food is raised as to how it tastes. Their goals include trying to curtail what they consider cruel methods of raising livestock and unsafe ways of growing food.

Those efforts are helping to fuel the right-to-farm movement in the Midwest, where the right has already won approval in North Dakota and Indiana. It goes next to Missouri voters in an Aug. 5 election. Similar measures passed both chambers of the Oklahoma Legislature earlier this year before dying in a conference committee. And they could soon spread elsewhere.

The uncertainty surrounding the proposals stems from the vague wording of the measures, which have yet to be tested in court.

Missouri's proposed constitutional amendment asks voters whether the right "to engage in farming and ranching practices shall be forever guaranteed."

Indiana's new measure — which was written into state law but not enshrined in the constitution— protects the rights of farmers to use "generally accepted" practices, including "the use of ever-changing technology." The North Dakota measure prohibits any law that "abridges the right of farmers and ranchers to employ agricultural technology, modern livestock production and ranching practices."

Supporters hope the wording provides a legal shield against initiatives that would restrict particular farming methods, such as those modeled after a California law setting minimum cage space for hens or policies in Florida and Ohio that bar tight pens for pregnant pigs. Others hope to pre-empt any proposals to ban genetically modified crops similar to ones recently passed in southern Oregon.

"Agriculture's had a lot folks that's been trying to come down on our farms and tell us what we can and cannot do," said Neal Bredehoeft, a corn and soybean farmer who supports the Missouri measure. He added: "This gives us a little bit of protection."

Bredehoeft gave $100 to the political group backing Missouri's ballot measure. His money is being mixed with five-figure checks from the state corn and pork associations, the Farm Bureau and businesses with strong financial stakes in rural America, such as electric cooperatives and a farm-credit organization.

They're preparing for an advertising blitz against a coalition that includes the Humane Society of the United States, the Sierra Club and rural groups that have battled for decades against corporate hog and poultry operations.

Opponents fear the right-to-farm measures could be cited by corporate farms to escape unwanted regulations against pollution and unsanitary conditions.

"This is a fight in each state," said Joe Maxwell, a former Missouri lieutenant governor who is the Humane Society's vice president of outreach and engagement.

Stopping the proposals at the ballot box "sends a message: Don't waste your money," he added.

North Dakota voters approved their right-to-farm measure by a two-thirds vote in 2012 after a relatively low-profile campaign in which the North Dakota Farm Bureau spent $158,000 promoting the measure. Opponents spent little.

The state Farm Bureau pursued the initiative after the Humane Society of the United States unsuccessfully pushed a measure two years earlier to abolish fenced hunting preserves in North Dakota.

Soon, agriculture leaders from Iowa to Idaho and numerous other places were inquiring about how to do something similar, said Jeffrey Missling, executive vice president of the North Dakota Farm Bureau.

A year ago, the North Dakota measure was a topic for discussion as legislative agriculture chairmen from across the U.S. gathered for a conference in Vancouver, Canada. The event by the State Agriculture and Rural Leaders Association was financed by dozens of agriculture businesses, including Archer Daniels Midland Co., Cargill, DuPont Pioneer, Deere & Co. and Tyson Foods. Among those present was Missouri Rep. Bill Reiboldt, a farmer who sponsored the right-to-farm amendment referred to this year's ballot by the Republican-led state Legislature.

The outcome of Missouri's vote could influence what happens next in the right-to-farm movement.

"There's a lot of rural people who would like to see it be a trend," said Carolyn Orr, executive secretary of the State Agriculture and Rural Leaders Association.

If it passes here, she added, "other state legislators will look at it more seriously."

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