Most of the patients don't qualify for government assistance, which covers dialysis for end-stage renal disease, because they are uninsured illegal immigrants, The Atlanta Journal-Constitution reported.
Without dialysis, people suffering from the disease can die within weeks, experts said.
The patients are now left with only a hospital emergency room for treatment, said Dorothy Leone-Glasser, president of the non-profit Advocates for Responsible Care.
"These patients are left in a very dangerous situation," she said. "We're asking them to decide, 'When do you think you're critical enough to go to the ER?'"
The patients had received dialysis at the public Grady Memorial Hospital's outpatient dialysis unit, which closed in 2009 after officials said it had been losing about $4 million a year, and the hospital is no longer licensed to provide outpatient dialysis.
Grady agreed last year to pay Fresenius Medical Care of Massachusetts $750,000 a year to provide dialysis for 25 uninsured immigrants.
But negotiations between Grady and Fresenius collapsed Wednesday, said Jane Kramer, a Fresenius spokeswoman.
The Journal-Constitution said a dozen patients were turned away from the Fresenius dialysis clinic Thursday morning.
Bineet Kaur, an immigrant from India who stayed in the United States after a visa expired, said she and other patients planned to go to Grady's emergency room Saturday to seek treatment.
"It's scary," she said. "We really don't know what's going to happen."