BOULDER — Millions of low-income expectant and nursing mothers and their children are facing a tough new challenge at grocery stores as coronavirus-panicked shoppers continue to snap up some of the most nutritious and inexpensive foods available.

More than 1.6 million women and 5.2 million infants and children receive benefits under the federal Women with Infants and Children, or WIC, program. But unlike more traditional food stamp programs, WIC money may only be spent on a narrow list of foods intended to provide the most nutrition at the lowest cost for taxpayers. If other people buy that food, WIC recipients can't use their benefits to buy something else.

"The people we serve are already stretched," said Commissioner David Hudson, national commander of the Salvation Army, which serves WIC recipients and other needy families. "When other people take more than they need, it stretches the system even more."

The challenges faced by WIC shoppers are the latest struggle for millions of Americans who are either already receiving federal food assistance or who are applying for it after losing their job. Panic shopping also hurts seniors on fixed incomes, experts said. Hudson said the Salvation Army, which serves 7,500 communities nationally, has seen demand double or and even triple in some areas since mass layoffs related to the coronavirus outbreak began in mid-March.

Experts said shoppers should avoid buying WIC-eligible foods if possible, because they have been carefully selected to provide the most nutrition at the lowest cost.

"If you only see one thing left on the shelf, leave it," said Melinda Morris, director of the Boulder County WIC program. "Please leave it for someone else."

While the specific products vary by state, WIC recipients may be limited to buying only white eggs, or specific types of plain canned beans and tuna, dried rice and whole-grain bread. In Colorado, for instance, WIC recipients are specifically limited to plain or vanilla yogurt, and banned from using their benefits to buy almond butter, most organic products and even baked beans.

Federal and state statistics show more people are now applying for WIC and food stamp benefits, although exact statistics are not yet available. Experts say they expect applications to skyrocket as millions of Americans who live paycheck-to-paycheck lose their jobs and seek government assistance.

Food banks have ramped up their services and schools are serving take-home meals for low-income families, but experts say the sheer size of programs like SNAP — what we commonly call food stamps — and WIC mean those federal programs will take on new importance in the coming months. About 40 million Americans receive food stamp benefits each month.

"We have seen a rapid increase in need, which is reflected in both our early SNAP application numbers, as well as a reported doubling in household assistance at Food Banks and pantries across the state," said Madlynn Ruble, a spokeswoman for the Colorado Department of Human Services.

Awareness of the issue has been spreading via social media, as some Americans share posts urging their friends to avoid shopping in the first few days of the month, when benefits are electronically deposited into recipients' accounts.

Morris and Hudson said there's no need to avoid shopping on those days, and instead suggested shoppers simply buy one week's worth of food at a time, instead of stockpiling supplies. With truckers still delivering plenty of food to grocery stores, there's no need to hoard, they said.

"People start buying everything imaginable and the people we serve don't have the assets necessary to get the supplies they need," Hudson said.