It was supposed to be a journey that would save her life, when U.S. immigration officials brought a 7-year-old girl named Ajlee from an asylum-seekers’ camp in the Mexican border city of Matamoros to an emergency room in Brownsville, Texas on Dec. 11. That same day, they also transported two women in need of urgent care: Yanet, with a possibly cancerous tumor, and Yoladiz, who is going blind from an untreated parasitic infection.

But the next day, all three were back in Mexico, living in tents in Matamoros with no access to the medical care they needed—despite agency guidelines requiring border officials to allow asylum-seekers with known medical issues to remain in the United States.

And attorneys and medical professionals say there are many more like them: individuals with health issues who’ve been caught up in the Trump Administration’s Migrant Protection Protocols, or MPP, which requires asylum-seekers to stay in Mexico while their cases are adjudicated in the U.S. Those with serious illnesses or disabilities should be exempt, but dozens have have been turned away at ports of entry and told to wait in Mexico because of MPP, according to seven lawyers and medical professionals who spoke to TIME. Human Rights First, a nonprofit, has documented several accounts of asylum-seekers, including pregnant women, children and adults with seizures, children with prosthetics and children with cerebral palsy, being returned to Tijuana, Mexicali, Juárez and Matamoros, which it calls a violation of the United States’ own immigration policies.

The MPP policy has faced legal challenges since it was implemented in January 2019, but in May, a federal appeals court allowed it to remain in place while a lawsuit challenging it continues. Meanwhile, the number of asylum-seekers who have waited on the Mexican side of the border for court dates has reached at least 56,000 since the end of November, according to the Transactional Records Access Clearinghouse, a data and research organization at Syracuse University.

The federal government’s rules state that members of “vulnerable” populations, including those with physical and mental health issues, are permitted to stay in the U.S. through the duration of their asylum cases once they present themselves to U.S. asylum officers. But Customs and Border Protection (CBP) officers have the final say, according to the agency’s guidelines.

The agency declined to comment on what further guidance or rules exist in determining who is considered vulnerable and therefor exempt from MPP. CBP spokesperson Richard Pauza in Laredo, Texas, tells TIME the agency cannot discuss individual cases for privacy reasons, but he says all claims are handled on a case-by-case basis.

Attorneys from Matamoros to Tijuana who spoke to TIME say the system leaves asylum-seekers at the mercy of whomever happens to be working at a port of entry on the day they arrive. It also means they must have a lawyer determined to fight for them.

“You have to be very insistent and you have to not give up,” Jodi Goodwin, a Texas attorney who volunteers in Matamoros, says of the lawyers who watch for asylum-seekers with clear medical or disability issues. When they meet one at a port of entry, they guide that person over the border and present them to CBP officials. Many agents aren’t familiar with the rules, she says. “You have to say that you want a supervisor, and you have to show [CBP] the guiding principles and make them understand what the law actually says,” says Goodwin. “You have to really be an advocate.”

But that doesn’t always work.

“I’ve seen uncontrolled, severe high blood pressure, people who had heart attacks, people who have had stomach cancer,” says Helen Perry, a nurse practitioner and executive director at Global Response Management, a nonprofit that provides volunteer emergency medical care in crisis areas. “There’s no consideration for the conditions that they’re being returned to. They’re just sent back so unceremoniously.”

In October, border officials allowed a 29-year-old deaf and non-verbal woman and some of her family into the U.S. from Matamoros, but only after a team of lawyers threatened to sue the agency. It was a major achievement, says Carrie O’Connor, an attorney who was involved in the weeks-long effort to persuade CBP that the family should be permitted to remain in the U.S.

Goodwin tells TIME she fought successfully to enable two children with down syndrome — one eight-month-old and one 10-year-old — to remain in the U.S. But she couldn’t persuade border officials to exempt a child with epilepsy and a child who had an amputated leg from being sent back to Mexico.

Once there, their chances of gaining access to advance medical care in Mexico are very limited, says Erika Pinheiro of Al Otro Lado, a legal aid nonprofit in Southern California. “It’s really difficult to access care in Mexico because of the type of status that [the Mexican government] gives people when they’re returned under MPP,” Pinheiro, who is based in Tijuana, tells TIME. “It’s like the same visa you would get if you’re visiting Mexico, so it’s difficult for people to use that to access the public health system.”

For those with health issues, the struggle is made worse by the perils of living in tents without basic services, in a notoriously dangerous city like Matamoros. The U.S. State Department urges Americans not to travel there for risk of kidnapping and crime.

In the U.S., although health care is expensive and can be difficult to access, resources are often donated by networks of doctors and other medical professionals throughout the country.

“In other areas of the world there would be a camp hospital or some local referral system when they need medical care,” says Perry. Perry runs the GRM project in Matamoros and was involved in Ajlee, Yanet and Yoladiz’s cases. “The reality for them is that literally 25 feet away across the river in the United States, we have all of the medical care that all three of these patients need,” Perry says.

Ajlee’s predicament became clear when a pediatrician from the U.S. visited the Matamoros encampment across the bridge from Brownsville in early December and determined that she needed surgery for a fistula — an internal abnormality that was causing her to defecate out of two locations and exposing her to serious infection. It likely was the result of colon surgery when she was a newborn.

Greg Shay, the doctor who examined her in Matamoros, accompanied lawyers when they presented Ajlee to border officials on Dec. 11, asking that she be taken to the U.S. to see a specialist. Ajlee, along with Yanet and Yodaliz, were taken to the Valley Baptist Medical Center’s emergency room in Brownsville, but Perry says the hospital could not help them.

“These aren’t conditions that need an emergency room,” Perry says. “These are conditions that need specialty care.” So the three were returned to Border Patrol custody and sent back to Matamoros the next day, Perry and Shay say.

Valley Baptist Medical Center did not immediately respond to TIME’s request for comment or for verification of the ER visit.

Yanet is aware she likely has uterine cancer, Perry says. “She knows that the prognosis of her condition is not good, but she also wants to join her family in Las Vegas.”

Yodaliz is going blind and needs to be treated for a parasite in her eye, Shay tells TIME. If she could access the proper care, she could be treated and lead a normal life, he says.

CPB officials refused to allow either woman to return to the United States, but on Tuesday, after receiving complaints from attorneys and advocates, they agreed to let Ajlee and her mother back in. That night, she slept in a Texas hotel room—a big leap from the weeks she’d spent living in a tent in Matamoros.

On Wednesday, Ajlee and her mother were flown to Baton Rouge, La., to meet with their sponsors, according to Kim Hunter, Ajlee’s attorney. Volunteer medical providers have ensured she will receive the medical care she needs there.

“It’s a mixed bag,” Hunter tells TIME. “Certainly we’re thrilled for our client, and her daughter.”

But noting the struggle it took to get the ailing girl to safety, she adds, “It shouldn’t take an army of lawyers and advocates to secure the release of one child who is in grave medical danger.”

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Write to Jasmine Aguilera at jasmine.aguilera@time.com.