The federal program - called the Special Supplemental Nutrition Program for Women, Infants and Children - gives vouchers to poor women and children to buy specific foods, such as milk, eggs, and bread. Each item's inclusion is based on medical research into the particular needs of the WIC population.
Five years ago, WIC began to include fruits and vegetables. White potatoes were omitted.
That's not because of any inherent nutritional deficiency, according to the U.S. Department of Agriculture, which runs WIC.
Rather, the nonpartisan Institute of Medicine, the health arm of the National Academy of Sciences, determined that the women and children in the WIC population of 8.7 million already eat enough white potatoes - or nearly enough.
Saying that the exclusion makes potatoes look unhealthy, the National Potato Council has been lobbying members of Congress - Democrats and Republicans, many of them from potato-growing states - to speak out.
This same group, with the help of Congress, took on the Obama administration in 2011 when the president wanted to limit potatoes in school lunches. He was unsuccessful.
Mark Szymanski, spokesman for the council, said the group was "encouraging Congress to reverse a policy not founded in good nutritional science or common sense. The USDA is singling out one item from the entire food basket and saying, 'Do not eat this because it's somehow lacking.' "
Sen. Susan Collins, a Republican from the potato-growing state of Maine, lauded the crop in a statement, saying, "The potato has more potassium than bananas, a food commonly associated with this nutrient, which is important for pregnant women and new mothers."
Meanwhile, nearly 100 nonprofit health and science organizations - including the American Pediatric Association, the American Medical Association, the National PTA, and the March of Dimes - have joined to ask Congress to stay out of scientific matters.
"We strongly urge you to oppose efforts to intervene in science-based rules regarding the federal child nutrition programs," the organizations wrote last month.
On Tuesday, around 100 pediatricians went to Capitol Hill to urge their representatives to back away from potatoes.
WIC officials, meanwhile, are livid.
"The National Potato Council has declared war on WIC," said the Rev. Douglas Greenaway, president and chief executive of WIC. "I would call it nothing more than industrial greed. This is all just a public-relations battle on the part of the potato industry."
Closer to home, advocates for the poor said they cannot countenance what they see as congressional overreach.
"It's unprecedented for Congress to step into this arena, based on lobbyist pressure," said Julie Zaebst, policy manager for the Greater Philadelphia Coalition Against Hunger. "It's just ridiculous."
Echoing Greenaway, Zaebst is worried that Congress was setting a "dangerous precedent for lobbyists from all industries to advocate for foods that wouldn't help families."
White potatoes themselves pose a problem, said Chelsea Anderson, a registered dietitian at St. Christopher's Hospital for Children in North Philadelphia, a neighborhood plagued by childhood obesity.
"White potatoes don't offer as many nutrients as other vegetables," she said. "And there's not a lot of healthy ways people prepare them."
Anderson's St. Christopher's colleague, pediatrician Hans Kersten, agreed, saying, "I often hear women say french fries are their favorite vegetable."
White potatoes need not be villainized, said Alison Ventura, professor of nutrition sciences at the Drexel University College of Nursing and Health Professions.
"They're a very healthy part of a diet," she said. "But young children's diets are much higher in french fries."
Among the Pennsylvania congressional delegation, just one representative signed letters supporting the inclusion of white potatoes in the WIC food package: Republican Charlie Dent, whose district includes portions of Lehigh, Dauphin, and Berks Counties.
His office issued a statement saying Dent describes white potatoes as "a healthy vegetable with good nutritional value offered at a reasonable cost."
Senbagam Virudachalam, a pediatrician at Children's Hospital of Philadelphia, said she does not believe that low-income people should not eat potatoes.
But, she added, "Americans in general consume more than they need in potatoes, and that's especially true in low-income communities."