Recipients of SNAP food assistance benefits across the country face a looming deadline: Come Nov. 1, their cards may not get refilled because of the government shutdown in Washington.

The Supplemental Nutrition Assistance Program, which serves nearly 42 million people each month, allocates money to states on a monthly basis. Benefits were largely uninterrupted over the past three weeks because funding for October was allocated to states before the shutdown began on Oct. 1.

But in a letter to SNAP state agency and regional directors on Oct. 10, the Department of Agriculture warned that there would not be enough funding to pay full SNAP benefits — also known as food stamps — in November if the shutdown persists.

Many states have announced that they plan to suspend SNAP benefits if the shutdown continues into next month. That could upend people’s ability to buy food on an unprecedented scale — the program has not lapsed during any government shutdown in recent history.

As Nov. 1 approaches, some state leaders are recommending that people turn to food banks or use their remaining benefits to buy nonperishable items.

“If you have accrued SNAP benefits from previous months on your account, use those funds now to buy shelf-stable foods that can last through November and beyond,” the Arkansas Department of Human Services says on its website.

But food banks say it will be impossible to fill the gap.

“There’s no way that our charitable food network or the system in this country can provide that much food overnight or quickly. It’s an impossible task,” said Catherine D’Amato, CEO of the Greater Boston Food Bank.

Her organization is already receiving calls from people asking where they can go to feed their families, she said. D’Amato estimated that suspending SNAP benefits would create a deficit of up to 56 million meals in Massachusetts in November.

At least one state, Pennsylvania, has already stopped issuing SNAP benefits. The state announced that “starting October 16, SNAP benefits will not be paid until the federal government shutdown ends and funds are released to PA.”

Texas, meanwhile, said next month’s SNAP benefits won’t be issued if the shutdown continues past Oct. 27. And in Wisconsin, SNAP recipients got a letter this week informing them that even their remaining funds from October may not carry over.

“Benefits may not be available in November,” the letter said. “This may include any funds remaining on your card at the end of October. You may want to use your benefits to stock up on food before the end of October.”

The state treasurers of Oregon and Massachusetts said Thursday on a press call that their states have no contingency plans for SNAP if the federal government doesn’t provide the funding. State budgets can’t afford to cover the full cost of people’s benefits, they added.

“At a time when the cost of groceries continues to go up, SNAP makes the difference between having enough and going hungry,” said Elizabeth Steiner, the Oregon state treasurer. “This decision on behalf of the federal government is an absolute abdication of its responsibility to families in Oregon and across the United States who are struggling to make ends meet.”

She added that “up until now, every administration, Republican or Democrat, has understood that feeding Americans is a fundamental responsibility of the federal government.”

In response to questions about SNAP funding, a spokesperson for the Department of Agriculture framed the issue as an inflection point for Democrats: “Continue to hold out for healthcare for illegals or reopen the government so mothers, babies, and the most vulnerable among us can receive timely WIC and SNAP allotments.”

In the shutdown standoff, congressional Democrats are holding out for certain health care provisions, including an extension of Affordable Care Act tax credits. Under federal law, those credits, along with other forms of federal health care, do not extend to immigrants who illegally reside in the U.S.

Democrats and Republicans will need to come to an agreement on a spending package in order to reopen the government.

WIC, which provides free food to low-income pregnant women, moms and children under 5, is similarly in danger of a funding shortfall in November because of the shutdown. Earlier this month, the Department of Agriculture used tax revenue to allocate $300 million to keep the program — known in full as the Special Supplemental Nutrition Program for Women, Infants and Children — afloat. However, many states worry that the funding could run out at the end of October.

Both WIC and SNAP participants use preloaded electronic cards to purchase food at participating grocery stores. For many low-income individuals and families, the benefits are their only means of affording staples like milk, eggs, cereal and vegetables.

“I’m worried about 16 million kids going home after school or being at home with their caregiver, and there’s no lunch and there’s no dinner,” said Christy Gleason, chief policy officer of Save the Children, a humanitarian organization. She added: “It may well be that a parent or a guardian is going without so that the kid can [eat].”

This story first appeared on NBCNews.com.