The partial government shutdown has frustrated tourists, delayed trash pickup in national parks and shut off the Smithsonian Zoo’s beloved panda cam.

But as the closure drags on with no end in sight, it’s also jeopardizing the welfare of some of America’s poorest families.

The Department of Housing and Urban Development is one of the seven agencies most directly affected by the standoff between President Donald Trump, who is demanding $5 billion in border wall funding, and congressional Democrats, who want to reopen the government without it. Since Dec. 22, the vast majority of federal housing employees have been forced to stay home without pay — prohibited from doing any work, including responding to emails.

Most of HUD’s routine enforcement activities have been suspended, including mandatory health and safety inspections of housing for low-income families, the elderly and people with disabilities, according to the shutdown contingency plan that HUD posted on its website. Public housing officials say they don’t know how long rental assistance payments will keep coming from the government, and a suspension could put millions of tenants at risk if the shutdown drags on into February. And if there are any problems in providing affordable housing grants to local and state governments, as well as nonprofit groups, there are few people on hand to resolve them, according to one furloughed staffer.

“Some of the money goes to housing for the most vulnerable households in this country,” said a HUD employee in a California field office who has been furloughed because of the shutdown and asked not to be named because he did not have permission to speak to the press.

“If there is the smallest glitch in the process, there’s going to be a problem," the employee said. "We work day in and day out to resolve these problems.”

The initial impact of the shutdown was muted as it began shortly before Christmas, typically a slow time for HUD and other federal agencies. But the standoff has now lasted nearly two weeks.

About 95 percent of HUD’s 7,500 employees have been furloughed without pay, according to HUD’s contingency plan. Those exempted from the furlough include staff members needed for emergency situations that pose “an imminent threat to the safety of human life or the protection of property.” That includes some housing and emergency services for the homeless, according to HUD’s contingency plan. But most work that requires hands-on processing and assistance has been put on hold, including activities that directly affect the well-being of low-income Americans.

“It’s been devastating — we have families and kids with asthma living where the mold situation is out of control,” said Cori Mackey, executive director of the Christian Activities Council, a social justice group in Hartford, Connecticut.

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Last week, the floor collapsed under the crutches of one Hartford tenant in a privately owned HUD-funded property, crashing into the ceiling of the neighbor living below her, Mackey said. When a handyman pulled up the floorboards, “it was just covered in black mold," she said.

Mackey said the building's tenants have been waiting for months for the results of HUD's most recent inspection. The tenants expected that their building would be given a failing score, which could potentially entitle them to short-term assistance to move elsewhere. The inspection's results were supposed to arrive by Dec. 31, but with the agency shut down, everything has been held up, leaving tenants stuck in crumbling housing, she said.

Basic questions about the shutdown remain unanswered, as both HUD staff and outside partners say they've been left in the dark. “There are some employees who are ‘excepted’ [from the furlough], but I don’t even know who they are,” Holly Salamido, president of American Federation of Government Employees Council 222, a labor union that represents HUD employees. “I can’t tell you what’s going on right now.”

Ellen Lurie Hoffman, federal policy director of the National Housing Trust, a nonprofit that advocates for affordable housing and owns HUD-funded rental properties, also said she lacked information from HUD.

“Previous administrations have had calls with industry stakeholders, saying, ‘Here’s what’s going to happen,’" she said. "None of that happened before this shutdown."

NBC News attempted to contact HUD for comment, but no one picked up the press line. An email to a spokesman produced an auto-reply that he was furloughed. An email sent to the general HUD public affairs account also went unanswered.

HUD’s own contingency plan described how poor families would bear the brunt of the shutdown. “A government shutdown would deeply impact the millions of families in need assisted by HUD programs,” the plan says. “Low-income families make up 72 percent of HUD-assisted households — and more than half of those receiving vouchers are elderly or persons with disabilities.”

If the shutdown drags into February — which would make it the longest closure in history, beating the 21-day shutdown under President Bill Clinton — housing officials and advocates say the consequences could potentially be dire for the millions of poor families who live in HUD-funded housing. Funds for basic public housing operations and housing vouchers are available through January, said Tim Kaiser, executive director of the ‎Public Housing Authorities Directors Association, which represents administrators of local housing authorities. But after that, he said, it’s unclear what will happen.

“They may have enough through February, but that’s not at all certain,” Kaiser said. “It’s unclear to me how much funding the department has available.”

Private landlords who participate in the Section 8 voucher program offer affordable housing to low-income tenants in return for monthly rental subsidies from local housing authorities funded by the federal government. If that money dries up, “landlords could start to evict people,” said Chad Williams, executive director of the Southern Nevada Regional Housing Authority. "We have never been in that situation."

While bigger housing authorities tend to have more money in reserve for emergency situations, smaller agencies — which often focus on serving seniors and people with disabilities and tend to be in smaller communities — may quickly fall short, Williams said. “For the smaller housing authorities, it’s just tragic.”

In addition, housing authorities could face delays in making critical repairs to faulty boilers or leaky roofs, according to the National Low Income Housing Coalition, an advocacy group.

Even after the government reopens, the shutdown could make the affordable housing crisis worse in the long term. The government closure is already putting new deals with private lenders and landlords on hold. In the future, private investors might think twice before doing business with the government, said Hoffman of the National Housing Trust. “It’s a much more difficult and risky proposition if the federal government isn’t holding up its end of the project.”

“The longer it lasts, the more direct the threats will be to low-income people."

By sidelining most HUD employees, the shutdown is also hurting morale at an agency already hobbled by staff cutbacks. “It’s saying you’re unessential, that your work doesn’t really matter,” said the HUD staff member in California. “I don’t think people have any awareness that it’s federal funds keeping these local programs running.”

Patrick Cano, a labor representative for HUD employees, said several furloughed members filed for unemployment on Thursday. “People are maxing out their credit cards," said Cano, president of AFGE for Local 911 in Chicago. “This is creating a lot of stress for their home life and their families.”

The consequences for both HUD staff and the people they serve will continue to mount if the standoff continues, housing advocates and officials say.

“The longer it lasts, the more direct the threats will be to low-income people,” said Michael Kane, executive director of the National Alliance of HUD Tenants, an advocacy group.