Animal rights groups are praising the Department of Health and Human Services secretary, Robert F. Kennedy Jr., for pushing the agency to reduce animal testing in drug development and invest in more humane alternatives, but does this mean the Republican Party — and the MAGA movement in particular — is embracing animal rights?

An intra-party battle over factory farming is coming to a head in Congress that will test this — and the divisions could derail passage of a new farm bill this fall. On one side is the agriculture secretary, Brooke Rollins, and more than 20 Republican members of Congress, mainly from Midwestern states, who are sponsoring the “Save Our Bacon Act,” which would prevent states from setting minimum confinement standards for livestock and from barring the sale of meat from out-of-state farms that do not comply with these rules.

On the other side is a group of Republicans — Congresswomen Anna Paulina Luna and Nancy Mace and Congressmen Byron Donalds and Mike Lawler, to name a few — who say states should have the right to set their own agriculture standards. At least 15 states have passed legislation regulating the use of gestation cages and other forms of tight animal confinement, including California, Massachusetts, Arizona, and Ohio.

More than 200 farmers from across the country and a tractor protest are heading to Capitol Hill on Wednesday to rally against the “Save Our Bacon Act” and any attempts to undermine state agricultural and farm animal welfare laws. One of the organizers, a lobbyist for the American Meat Producers Association, Holly Bice, tells The New York Sun that she expects this will be the largest American farmer protest in recent history. Members of Congress from both sides of the aisle are expected to speak, though Ms. Bice says the government shutdown may complicate plans.

The animal welfare movement is often coded left-wing, but opposition to factory farming and animal testing cuts across partisan lines. By bringing Mr. Kennedy and the MAHA movement into the MAGA fold, President Trump lured traditionally left-wing constituencies like crunchy organic food moms into the Republican Party. Even PETA is praising Mr. Kennedy’s moves to phase out animal testing.

“We rate what RFK Jr. has pledged to do very highly,” the founder of PETA, Ingrid Newkirk, tells the Sun. When asked whether the Trump administration is doing more for animal rights than previous administrations, Ms. Newkirk said, “Yes, on the animal experimentation front.”

Yet while Mr. Kennedy railed against factory farming when he was running for president, Ms. Rollins is the agriculture secretary, and she is a friend to Big Ag. At her confirmation hearing, Ms. Rollins assured Senator Joni Ernst of Iowa that she would work to repeal California’s Proposition 12, which prohibits the sale of pork, veal, and eggs from animals kept in tight confinement. The Trump administration sued California in July over Proposition 12, saying the cage-free egg requirement is driving up the cost of eggs nationwide and oversteps federal authority. The suit is pending.

“Kennedy’s got a great history on animal welfare,” a conservative animal rights lobbyist, Marty Irby, tells the Sun. “There’s definitely a big divide. I think the Trump administration has been extremely friendly and much better than the Biden administration on companion animals and animal testing.”

“But on farm animal welfare, they’ve been, I would say, hostile in that department,” Mr. Irby says.

On the campaign trail, Mr. Trump often said, “We love our farmers.” He also wants food prices to be lower. He wants farm states in the Midwest to remain largely Republican-controlled. Those who oppose Proposition 12 and other state laws that bar gestation cages and the sale of meat from animals raised in them say these laws increase the cost of meat and hurt farmers.

The chief executive of the National Pork Producers Council, Bryan Humphreys, told the Sun earlier this year that the laws “defy common sense” and are authored by “vegan activists who make no secret of their zealous efforts to end animal agriculture.” The National Pork Producers Council sued California in 2019 over Proposition 12, but the Supreme Court upheld the law on a states’ rights basis in an opinion by Justice Gorsuch.

It’s easy to paint animal welfare activists as radical vegans, but the Republican contingent opposed to factory farming is more of the carnivore diet, clean eating types like Mr. Kennedy. “Like most people, I eat meat and also support humane animal treatment,” a MAGA influencer, Laura Loomer, a close associate of Mr. Trump, tells the Sun. “I support states’ rights.”

“I’m proud that Republicans have been leading the way in Washington on many animal welfare issues, especially on ending billions in federal subsidies for cruel and unnecessary testing on animals like dogs and cats,” Ms. Loomer says.

With the slim GOP majority in Congress and a growing faction of Republicans caring about factory farming, animal welfare, and the role food plays in health, Ms. Bice says any attempt to slip the “Save Our Bacon Act” or similar legislation into a farm bill or funding resolution could kill it. “This is a poison pill,” she says.

Fourteen Republican members of Congress last month signed a letter to the chairman of the House Committee on Agriculture arguing that the “Save Our Bacon Act” and similar legislation is “sweeping federal overreach,” will hurt family farmers, and will only help Big Ag producers. MAGA loyalists like Representatives Anna Paulina Luna and Byron Donalds were among the signers.

The number of family farms is steadily declining, according to USDA figures, and the size of farms is increasing, meaning Big Ag is taking over a larger share of the agriculture market. The top four egg producers control half the American egg market. The top four pork producers control nearly 70 percent of the market. The largest pork producer is Chinese-owned Smithfield Foods.

The GOP letter says the bill “would erode states’ rights, undermine family farmers, and expand foreign influence over U.S. food production.” It doesn’t frame this as an animal rights issue but calls Smithfield Foods’s 23 percent stake in the American pork market “disturbing” and argues that the “Save Our Bacon Act” will only “consolidate the influence of such foreign entities.”

Ms. Bice says the legislation will also hurt farmers who invested millions of dollars to revamp their farms to comply with Proposition 12 and other state laws. Some of these farmers will be at Washington, D.C., on Wednesday to make their voices heard.

“Republicans should really take animal welfare back as a conservative issue,” Ms. Bice says. “It polls well, and it helps win elections.”