BOSTON — With deadlines to apply for federal grants fast approaching, the Trump administration is pledging to make good on threats to withhold funding for cities and towns that refuse to detain immigrants suspected of living in the country illegally.

President Donald Trump, a Republican, has vowed to pull back federal funding for so-called “sanctuary cities” like Boston and Lawrence, and issued an executive order Jan. 25 directing the Department of Homeland Security to begin that process.

Attorney General Jeff Sessions appears to be following through on those threats. He has issued new guidelines for U.S. Justice Department grant money that require local police to open their jails to federal immigration officers and assist with enforcement.

“We cannot continue giving taxpayer money to cities that actively undermine the safety and efficacy of federal law enforcement and actively frustrate efforts to reduce crime in their own cities,” Sessions told reporters last week at an event in Miami, Florida.

Two grants that could be withheld are the Edward Byrne Memorial Justice Assistance Grant, or JAG, which provides funding to support local law enforcement efforts, and the Justice Department’s Office of Violence Against Women grants.

Under the new policy, those grants will be available only to communities that comply with a federal statute requiring them to provide immigration information about individuals to the federal government and give federal immigration authorities access to local jails.

They will also need to provide the Department of Homeland Security at least 48 hours’ notice before releasing an undocumented immigrant wanted by federal authorities.

To date, six communities in Massachusetts — Boston, Somerville, Cambridge, Amherst, Northampton, Lawrence and most recently Salem — have declared themselves sanctuaries or passed similar laws.

Rules vary by community. In Salem, police will not go out of their way to check people’s immigration status. A recent ordinance, however, doesn’t keep them from cooperating with federal authorities. In Lawrence, local police will not hold immigrants suspected of illegally living in the United States unless a criminal warrant has been issued.

Millions of dollars are at stake for cities and towns in Massachusetts and elsewhere under Session’s new directive.

In the previous fiscal year that ended June 30, Massachusetts cities and towns received $1,751,120 through the JAG program, according to federal data.

Salem received $11,737, the first of a three-year allocation. Lawrence received $66,963; Northampton $11,189; Cambridge $28,579; Somerville $17,216 and Boston $417,809.

Applications for the grants in fiscal year 2017 are due Sept. 5. The program is named for Edward Byrne, a New York City police officer who was killed in the line of duty in 1988. He was protecting a Guyanese immigrant who had reported a crime. 

The money is generally used to hire police officers and purchase SWAT equipment, vehicles, Tasers, radios and other items, according to law enforcement officials. 

The OVW grants, which will be announced in coming weeks, are given to communities and organizations working to prevent domestic violence, sexual assault and abuse.

Last year, Salem received $450,000 from a statewide allocation of more than $9 million, according to federal data. Most the grant money was awarded to state agencies and nonprofits such as Jane Doe, Inc., which works with abused and battered women.

Salem officials say they believe they are on solid legal ground, and won’t lose funding.

Dominick Pangallo, a spokesman for Mayor Kim Driscoll, said the city’s laws and policies regarding cooperation with federal immigration officers “expressly state that all federal laws are to be observed and information, when required under federal law and constitutionally requested, is to be shared.”

“We’re not violating any laws,” Salem police Chief Mary Butler said. “We communicating with federal authorities and not holding anything back. So I think we’re on firm ground.”

Butler said Salem police regularly cooperate with federal officials when someone who is arrested is also sought by U.S. Immigrations and Customs Enforcement officers.

But she doesn’t want the city’s police officers to act as immigration agents.

“That’s not our job,” she said. “We have a community to police and if we’re going to build trust we can’t be in a situation where we’re asking officers to do something that’s beyond the scope of their authority.”

Neither spokespersons for Lawrence Mayor Dan Rivera or Somerville Mayor Joe Curtatone returned phone calls seeking comment for this story. Boston Mayor Marty Walsh’s press office also declined to comment.

Immigrant advocates and some Democratic lawmakers say requiring local police to cooperate with federal immigration agents makes communities less safe because it dissuades people from reporting crime for fear of arrest and deportation.

Critics say the move shields dangerous criminals from arrest. They support the Trump administration’s get-tough approach to forcing cities and towns to cooperate. 

“There are definitely cities and towns in Massachusetts that will lost federal funding if they don’t change what they are doing,” said Jessica Vaughan, director of policy studies for the Center for Immigration Studies, a conservative Washington think tank.

Sessions’ new policy is backed by a 1996 law that requires law enforcement grant recipients to comply with immigration laws but hasn’t been enforced, she said. 

A spokesman for U.S. Justice Department didn’t return a call seeking comment.

To be sure, Session’s threats to defund all sanctuary cities faces legal challenges over constitutional provisions that prevent the federal government from taking punitive actions against states and cities, observers say.

Chicago filed a federal lawsuit against the Justice Department last week over the new grant money stipulations. Chicago Mayor Rahm Emanuel, a Democrat, told reporters at a briefing on the lawsuit that his city “will not be blackmailed into changing our values.”

On Wednesday, a federal court judge blocked Texas from implementing a new law that would have banned cities and towns from passing local sanctuary city ordinances.

Vaughn said she doesn’t believe such legal challenges will survive judicial scrutiny.

“There will be lawsuits, for sure,” she said. “But I doubt they will be successful.”

Meanwhile, immigrant advocates are pressuring lawmakers to declare Massachusetts a “sanctuary state” that bars local police from detaining people living here illegally.

One proposal backed by more than 60 lawmakers — including Lawrence Democratic Reps. Juana Matias and Frank Moran, and Sen. Barbara L’Italien, D-Andover — would stop police from holding undocumented immigrants without an arrest warrant

Gov. Charlie Baker, a Republican, has threatened to veto the bill if it reaches his desk. Baker has said he doesn’t oppose cities and towns that declare themselves sanctuaries, but the state shouldn’t impose a blanket law.

He has filed legislation to give police the power to detain illegal immigrants on behalf of federal authorities if they pose a threat to national security or other serious crimes. 

Christian M. Wade covers the Massachusetts Statehouse for North of Boston Media Group’s newspapers and websites. Email him at cwade@cnhi.com.