Dismaying immigrants and advocates, U.S. Citizenship and Immigration Service (USCIS) sent out letters saying the agency will no longer consider most deferrals of deportation for people with serious medical conditions, documents show.

The agency is now saying those decisions will be made by another agency: U.S. Immigration and Customs Enforcement (ICE).

That was not made clear to Boston-area immigrants who received the denial letters last week. Advocates said they received no formal announcement of a change in policy.

The small program known as "medical deferred action" allows people to remain in the U.S. for two-year periods if they can prove extreme medical need. Many of the people affected by the policy change came to the U.S. through a visa or other permitted status and are requesting to stay beyond those terms to receive medical treatment.

Hours after this story was published Monday, a USCIS spokeswoman responded to several requests for clarification about the policy shift to say that "medical deferred action requests are now submitted to ICE for consideration."

This shift in policy has not been announced publicly by the government, and immigration advocates and attorneys question why this new process wasn't mentioned in the denial letters.

In response to a WBUR request for details, a spokesman for ICE sent this statement late Tuesday morning: "As with any request for deferred action, ICE reviews each case on its own merits and exercises appropriate discretion after reviewing all the facts involved."

Anthony Marino, director of legal services for the Irish International Immigrant Center (IIIC), explained that up until now, federal immigration officials would routinely permit eligible sick people to stay in the country under this program. But last week, five of his clients — who he says would have typically qualified — received what appeared to be template denial letters with the exact same language.

"The denials say specifically that the immigration service is just no longer considering deferring action at all in these cases, which would be a first in decades," he said.

Marino added many of the affected clients at the center are families whose children are battling cancer, cystic fibrosis, HIV, cerebral palsy, muscular dystrophy and epilepsy.

According to the apparent form letters, USCIS field offices “no longer consider deferred action requests, except those made according to the U.S. Department of Homeland Security (DHS) policies for certain military members, enlistees, and their families.”

The dated letters notified families they must leave the country within 33 days of the government's writing. Otherwise, they face removal and exclusion from the U.S. for several years. Legal advocates across the country have reported clients receiving similar denial letters.

“This attack on children and their families is inhumane and unjust,” said Ronnie Millar, executive director of IIIC, in a press release. “These families are all here receiving treatment that is unavailable in their home countries, and our government has issued them a death sentence.”

In a statement, Marilu Cabrera, a public affairs officer with USCIS, confirmed that field offices will no longer consider non-military requests for deferred action and instead, will direct resources to administering "our nation's lawful immigration system."

The statement went on to say that this reallocation of resources does not affect Deferred Action for Childhood Arrivals (DACA) or other deferred action requests processed at USCIS service centers.

The IIIC held a noon press conference Monday about the government's decision, where some affected families were in attendance.