Massachusetts Sens. Ed Markey and Elizabeth Warren are demanding that U.S. Customs and Border Protection (CBP) withdraw a plan to deploy agents -- including some that are specially trained in SWAT-like tactics -- to Boston and other American cities that have chosen not to cooperate with President Trump's immigration policies.

A U.S. Department of Homeland Security (DHS) official in Boston has confirmed that some of those officers are already working in Boston with local U.S. Immigration and Customs Enforcement (ICE) officials.

In a letter to the heads of CBP, DHS and ICE, Markey and Warren call the initiative "unnecessary, unwelcome, dangerous, menacing, retaliatory and unlikely to achieve its stated goal."

Specifically, Markey and Warren protest the use of heavily-armed Border Patrol Tactical Unit (BORTAC) officers, which the New York Times reports will be deployed to certain cities as part of the operation.

They go on to say BORTAC agents are supposed to be used to handle dangerous situations outside the normal scope of Border Patrol agent duties — not for "run-of-the-mill immigration arrests" in some of America's largest cities.

In closing, Warren and Markey asked federal officials to answer the following questions by Feb. 24, 2020:

How many of the CBP personnel deployed to assist ICE are BORTAC members? In which communities will these BORTAC members be deployed? What are the specific orders given to the BORTAC teams, and what are their specific rules of engagement while deployed in American cities? What is the chain of command for deployed BORTAC teams?

Boston and other Massachusetts communities, along with cities and towns across the country, limit the level of assistance local low enforcement can give federal authorities in immigration matters. Often referred to as "sanctuary cities," these policies have come under fire by the Trump administration.

In a statement released Friday, acting ICE Director Matthew Albence said the specially trained CBP officials would assist ICE agents in the field.

"As we have noted for years, in jurisdictions where we are not allowed to assume custody of aliens from jails, our officers are forced to make at-large arrests of criminal aliens who have been released into communities," Albence said in the release. "This effort requires a significant amount of additional time and resources. When sanctuary cities release these criminals back to the street, it increases the occurrence of preventable crimes, and more importantly, preventable victims.”

Clarification: In their letter, Sens. Markey and Warren refer to BORTAC agents being deployed to Boston. WBUR has not independently confirmed the presence of BORTAC agents in Boston, but has confirmed the presence of specially trained, tactical CBP officials. This story has been updated to reflect that.