Additionally, People's is being investigated by state labor officials after three employees filed complaints about wage-and-hour violations. The state Department of Labor, Licensing and Regulation said it cannot provide details of the complaints because they are confidential.

The nonprofit faces lawsuits from creditors, including Baltimore's government, which says it is owed more than $18,000. A hearing is scheduled for July 23, according to online court records.

Other claims have been filed by Gant Brunnett Architects of Baltimore, for $2,500, and AMJ Lawn and Landscaping of Pasadena, for $3,897.20 regarding alleged nonpayment for snow removal.

In recent months, some People's clinics were closed on some days or offered reduced hours.

"It may have been going on for some time," Sharfstein said. "That's a problem. We expect clinics to be open."

People's is one of 16 federally qualified health center groups that operate 136 clinics around the state, according to the Mid-Atlantic Association of Community Health Centers. There are more than 1,100 such groups nationwide, according to the National Association of Community Health Centers.

Hardly any of them ever close their doors, said Dan Hawkins, the national association's senior vice president for policy and research. Generally, around four or five a year threaten to close, but other groups are formed to run the clinics or existing groups step in. Occasionally, patients are sent to other centers.

"The demise of a health center organization is an exceedingly rare event," he said. "Complete closure is even more so. I don't know about People's specifically, but I'd be surprised to hear there was no continuation of services."

He said it's in the interest of the government and the community to keep the centers open because there are few other resources for patients who are typically low-income. About 80 percent don't have insurance or have Medicaid and would otherwise go to the local emergency department, where care is expensive and the costs are passed on to taxpayers directly — or, in Maryland, as higher hospital rates.

The Affordable Care Act provided $11 billion to offset the cost, though some of that money has already been cut. Federal grants now make up about 17 percent of the centers' budgets. Medicaid dollars make up about 29 percent and the rest comes from state, local and private money, as well as some other federal programs for those with HIV and or children, according to Leighton Ku, a professor of health policy at George Washington University who has been studying the impact of health reform on the centers.

He said the federal money runs out next year, and that could put more centers in peril. But funding is available now, making it "a little surprising" that centers were having trouble accessing grants.

"That doesn't mean all centers don't struggle," Ku said, while noting that he was not familiar with People's problems. "Every year they increase size and capacity. They need more space and more staff, and there's a shortage of primary care physicians. … They've had to learn about electronic medical records and other standards. So there are challenges, but they've done pretty well."

Baltimore City and Anne Arundel County officials say they're working to identify new health care providers for People's patients.

Other clinics in Baltimore are willing to take over the People's sites or see their patients, said Tracy Douglas-Wheeler, chief operating officer of the Mid-Atlantic Association of Health Centers.

"All of the other federally qualified health centers in the city are willing and able to do whatever it takes to handle and manage any individual who needs primary health care and impacted by the People's closure," she said. "For now, People's is directing patients to the other clinics."

Among those who must look for a new provider is Sadia Amjad of Glen Burnie, a Medicaid recipient who is expecting her first baby next month. At a checkup Wednesday at the Brooklyn Park clinic, she learned of its impending closure.

Her doctor promised that by next week, she'll have a referral to a new physician. Amjad hopes so, but she said she likes her doctor and will miss her.

"I'm a little worried about it, because she's good," she said.

Baltimore Sun reporter Nayana Davis contributed to this article.