June 5, 2014 6:12 AM EDT

As school nutrition officials gathered around a conference table in the Eisenhower Executive Office Building on May 27, Michelle Obama’s trademark hug-a-stranger vibe was notably absent. “This is unacceptable,” she said curtly. “It’s unacceptable to me not just as First Lady but also as a mother.”

What was irritating Obama was an attempt by the Republican-controlled House of Representatives to ease school nutrition standards she helped pass in 2010. “The stakes couldn’t be higher on this issue,” Obama said, noting that 1 in 3 U.S. children will develop Type 2 diabetes. “The last thing we can afford to do right now is play politics with our kids’ health.”

But in the nation’s capital, even kids’ health can be political, as billions of dollars are at stake depending on what goes into school lunches. In Congress, the interests of farmers and food companies regularly clash with the concerns of parents and the nutritional recommendations of the USDA. Nor is the school-lunch fight new: the standards the First Lady is fighting to preserve have already been weakened once before in response to food-industry opposition.

This was, to some extent, inevitable. Ever since she made school meals a signature issue early in the President’s first term, the First Lady has tried to join forces with the food industry on initiatives to shrink package sizes and include healthier fare on kids’ menus. In exchange, she has moderated her criticism of junk food and acknowledged that there is nothing wrong with the occasional indulgence. (She notably handed out sugar-sweet marshmallow Peeps at the annual White House Easter Egg Roll and has called french fries a favorite food.)

But that tenuous alliance has been breaking down as House Republicans, food-industry groups and other stakeholders have pushed to allow schools to delay the new federal standards. Among the changes, which affect some 50 million public-school students: full-sugar sodas and junk food are being removed from school vending machines, low-fat replaces whole milk, and every child is required to have at least one serving of fruits or vegetables per meal (see chart, right).

The USDA says 90% of schools are already meeting the standards, but the First Lady’s critics argue that the rules are inflexible and full compliance is too costly for some districts. Some accuse her of running a nanny state by trying to dictate what kids eat. Children accustomed to Tater Tots, they say, are unlikely to start wolfing down kale. And they point to sporadic lunchtime rebellions–such as students in one New Mexico district chucking whole-wheat tortillas in the trash–as evidence.

“They are driving students away from healthy school meals while threatening to bankrupt many school meal programs,” says Leah Schmidt, president of the School Nutrition Association, which represents 55,000 school nutritionists. Her group–whose advisory board includes representatives from Barilla, ConAgra, General Mills and PepsiCo–claims the new standards have caused 1 million kids to eat lunch off campus this year.

Supporters of the new standards say adjusting kids’ palates takes time but is worth the effort. They see the push for a delay as the first step on the road to a complete repeal. “It creates a loophole that could allow people to game the system,” says Agriculture Secretary Tom Vilsack. The First Lady’s allies insist the $4.5 billion Congress allocated in 2010 provides plenty of help to schools that have found the cost of bringing in fresh foods prohibitive.

More lunchroom trading is likely. In 2011, Republicans held up funding for the new rules, which are being put into effect gradually over 12 years, in order to extract concessions favorable to the potato and cheese industries. The result: even the revised standards count the small amount of tomato sauce in pizza as a vegetable serving and allow french fries (albeit the new baked ones) to be served as often as a school wishes. Spa cuisine it is not.

This appears in the June 16, 2014 issue of TIME.

Contact us at editors@time.com.

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