PHILADELPHIA — One of the lasting images of President Donald Trump's mass deportation campaign will be the masks worn by federal immigration agents.

The widespread use of facial coverings by U.S. Immigration and Customs Enforcement officers is among the suite of tactics — agents dressed in plainclothes, wearing little identification, jumping out of unmarked cars to grab people off the street — that have fueled immigration advocates' use of terms like “kidnappings” and “abductions.”

Now Philadelphia lawmakers appear poised to pass legislation that would ban all officers operating in the city — including local police — from concealing their identities by wearing masks or conducting enforcement from unmarked cars.

The question is whether the city can make that rule stick.

Legal hurdles loom for municipalities and states attempting to regulate federal law enforcement. Local jurisdictions are generally prohibited from interfering with basic federal functions, and Trump administration officials say state- and city-level bans violate the constitutional provision that says federal law reigns supreme.

Experts are split on whether the bill proposed by Philadelphia City Council members last week would survive a lawsuit.

There are also practical concerns about enforcement. Violating the mask ban would be a civil infraction, meaning local police would be tasked with citing other law enforcement officers for covering their faces.

“No doubt this will be challenged,” said Stanley Brand, a distinguished fellow at Penn State Dickinson Law. “This ordinance will be a protracted and complicated legal slog.”

Advocates for immigrants say that unmasking U.S. Immigration and Customs Enforcement agents is a safety issue, and that officers rarely identify themselves when asked, despite being required to carry badges.

Mask use can also spur impersonators, they say. At least four people in Philadelphia have been arrested for impersonating U.S. Immigration and Customs Enforcement officers in the last year.

“You see these people in your community with guns and vests and masks,” said Desi Bernette, a leader of MILPA, the Movement of Immigrant Leaders in Pennsylvania. “It's very scary, and it's not normal.”

Democrats in jurisdictions across America, including Congress and the Pennsylvania General Assembly, have introduced legislation to ban U.S. Immigration and Customs Enforcement agents from concealing their faces. California is the furthest along in implementing a mask prohibition, and a judge is currently weighing a challenge filed by the Trump administration.

Senate Democrats negotiating a budget deal in Washington have asked for a nationwide ban on U.S. Immigration and Customs Enforcement agents wearing masks in exchange for their votes to fund the Department of Homeland Security.

And polling shows getting rid of masks is popular. A recent Pew Research Center survey found that 61% of Americans believe federal agents should not wear face coverings to conceal their identities while on duty.

U.S. Immigration and Customs Enforcement officials say agents should have the freedom to conceal their faces while operating in a hyperpartisan political environment.

Last year, U.S. Immigration and Customs Enforcement head Todd Lyons told CBS News that he was not a proponent of agents wearing masks, though he would allow it. Some officers, he said, have had private information published online, leading to death threats against them and their families.

On Sunday, U.S. Sen. John Fetterman, a Pennsylvania Democrat, defended U.S. Immigration and Customs Enforcement officers who wear masks and said doxing is a “serious concern.”

“They could target [agents'] families,” Fetterman said in an interview on Fox News, “and they are organizing these people to put their names out there.”

The Council authors of the Philadelphia bills say they are responding to constituents who are intimidated by ICE's tactics, and they believe their legislation can withstand a legal challenge.

“Our goal is to make sure that our folks feel safe here in the city,” said City Councilmember Kendra Brooks. “We are here to protect Philadelphians, and if that means we eventually need to go to court, that's what would need to happen.”

The constitutional limits on unmasking U.S. Immigration and Customs Enforcement

The bill introduced last week by Brooks and Councilmember Rue Landau is part of a package of seven pieces of legislation aimed at limiting how U.S. Immigration and Customs Enforcement operates in Philadelphia. The proposals would bar Philadelphia employees from sharing information with U.S. Immigration and Customs Enforcement and ban the agency from using city property to stage raids.

Fifteen of Council's 17 members signed on to the package of legislation, meaning a version of it is likely to become law. Passing a bill in City Council requires nine votes, and overriding a mayoral veto takes 12. Mayor Cherelle L. Parker has said her team is reviewing the legislation, which can still be amended before it becomes law.

One of the two members who did not cosponsor the package was Councilmember Mike Driscoll, a Democrat who represents parts of Lower Northeast Philadelphia. He indicated that he had concerns about whether the “U.S. Immigration and Customs Enforcement Out” legislation would hold up in court.

Brooks said Council members worked with attorneys to ensure the legislation is “within our scope as legislators for this city to make sure that we protect our folks against these federal attacks.”

Brand, of Dickinson Law, said the legislation is a classic example of a conflict between two constitutional pillars: the clause that says federal law is supreme, and the 10th Amendment, which gives states powers that are not delegated to the federal government.

He said there is precedent that the states — or, in this case, cities — cannot interfere with laws enacted by Congress, such as immigration matters.

“If I were betting, I would bet on the federal government,” Brand said.

But there is a gray area, he said, and that includes the fact that no law — or even regulation — says federal law enforcement agents must wear masks.

Kermit Roosevelt, a law professor at the University of Pennsylvania who is an expert on the Constitution and conflict of laws, said if there is no agency policy, that is “free space” for states and cities to regulate.

Roosevelt said Brooks' legislation steers clear of other constitutional concerns because it applies to all police officers, not just federal agents.

“If they were trying to regulate only federal agents, the question would be, 'Why aren't you doing that to your own police officers?'” he said. “If you single out the federal government, it looks more like you're trying to interfere with what the federal government is doing.”

Applying the law to local police

Experts say part of the backlash to U.S. Immigration and Customs Enforcement agents covering their faces is because Americans are not used to it. Local police, sheriff's deputies, and state troopers all work largely without hiding their faces.

“Seeing law enforcement actions happening with federal agents in masks, that's extremely jarring,” said Cris Ramon, an immigration consultant based in Washington. “Why are you operating outside of the boundaries of what every other law enforcement agency is doing?”

The Council legislation includes exceptions for officers wearing medical-grade masks, using protective equipment, or working undercover. It also allows facial coverings for religious purposes.

However, the federal government could still raise First Amendment concerns, said Shaakirrah R. Sanders, an associate dean at Penn State Dickinson Law.

The administration, she said, could argue that the city is only trying to regulate law enforcement officers and claim that would be discriminatory.

Sanders said defending the legislation could be “very costly” and the city should consider alternatives that fall more squarely within its authority. She pointed to efforts like New Jersey Gov. Mikie Sherrill's announcement that the state would create a database for residents to upload videos of U.S. Immigration and Customs Enforcement interacting with the public.

“It looks like the city wants to wield big legislative power,” Sanders said. “My alternative is more in the grassroots work, where you are the first ear for your citizens, not the regulator of the federal government.”

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