When New York City launched the nation's largest municipal ID program, advocates said it would give immigrants in the country illegally access to bank accounts and city services.

"They could go visit a loved one in the hospital, they could go visit their child's teacher," Mayor Bill De Blasio said at a press conference earlier this month. "If they had an interaction with a police officer, there was an ID recognized by the NYPD. It was a very basic concept."

By most metrics, the IDNYC card has been a resounding success. New York City has issued roughly 900,000 ID cards since last year. No one knows exactly how many IDNYC cardholders are in the country illegally, although the number is probably in the hundreds of thousands. But now, with President-Elect Donald Trump coming to power, there are concerns that the program could backfire.

During his campaign, Trump talked about deporting millions of immigrants in the country illegally. New York City leaders want to protect the people who've signed up for ID cards by deleting the personal information the city collected about those cardholders — including names, addresses and social security numbers.

"The reason people were willing to trust us was we made very clear that there would never be a situation where it would lead to their deportation," said de Blasio, a Democrat. "And we're going to keep that pledge, and it's also part of our law."

But two state lawmakers are suing to stop the city from deleting those records.

"Our concern is really for the safety and security of the citizens that we represent," says including Nicole Malliotakis, a Republican who represents Staten Island and parts of Brooklyn. "You know, why are we issuing 900,000 ID cards — whether it's to citizens, legal residents or illegal immigrants — and then destroying all the information? We don't know how those individuals obtained that identity."

A court has ordered New York to preserve those records — at least until a hearing on Wednesday.

"The city may have a fight on its hands — a fight that was entirely avoidable," says Jonathan Blazer, a lawyer with the American Civil Liberties Union.

He says most other cities that have launched successful ID programs — including San Francisco and Oakland — handle sensitive information differently. Those cities require applicants to show documents that prove their identity and residency, and they inspect them rigorously, but they don't keep the information on file. New York says it will no longer retain sensitive information about new applicants.

The city of Elizabeth, N.J., approved their program in October. Mayor Chris Bollwage, a Democrat, doubts the new administration will focus on these programs.

"I don't believe the Trump administration is going to start sending out subpoenas to all of these individual cities who've given out municipal IDs," Bollwage says. "I would hope the Trump administration focuses on issues of much more importance than that."

The majority of the population in Elizabeth is Hispanic. And it's estimated that the city is home to thousands of immigrants who entered the country illegally. Vicente Jadan works in construction, and volunteers for the immigrant rights group, Make the Road New Jersey. Jadan says he's eager to sign up for the new city ID.

"Especially because we need it to bank here, even to open a bank account," Jadan says. "Without an ID you can't do anything."

Copyright 2016 NPR. To see more, visit http://www.npr.org/.