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Researchers at Syracuse University are gearing up to take Immigration and Customs Enforcement officials to court now that the agency is no longer releasing information it had routinely disclosed under public records laws for the last 13 years.

Susan Long, co-director of Syracuse University’s Transactional Records Access Clearinghouse, said on Thursday that the group was preparing a court challenge to compel ICE to release information associated with "detainer" forms the agency uses to hold immigrants who have committed or are accused of crimes.

“They have cut way back on the details they provided on detainers — basically the info that would allow an examination of the agency’s performance, and whether it is achieving its stated goals,” Long told NBC News Thursday. “We are preparing to file a lawsuit unless ICE reverses itself on our administrative appeal and turns the data over.”

A sheriff's deputy talks to an immigration detainee in a high security housing unit at the Theo Lacy Facility, a county jail which also houses immigration detainees arrested by the U.S. Immigration and Customs Enforcement (ICE) in Orange, California on March 14, 2017. Robyn Beck / AFP - Getty Images, file

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In the past, the Syracuse clearinghouse had received information from ICE about individuals’ arrests, detainment locations, detainment dates and deportation dates, should an immigrant be deported, Long said. The agency also previously released criminal histories, including charges, convictions, sentences and corresponding dates.

But in a Jan. 10 response to a Freedom of Information Act (FOIA) request seeking detainer information covering October 2014 to November 2016, fields of information were missing.

Now, the group only receives information as to the nationality, gender and citizenship of a given immigrant, as well as the date a detainer was prepared, the law enforcement agency it was issued to and local body's response.

ICE, Long said, claimed the previous 13 years of disclosures weren't mandatory.

An ICE spokesperson told NBC News Thursday, "We can't comment on any potential litigation actions."

A former senior ICE official under Presidents George W. Bush and Barack Obama, whose name NBC News is withholding because his current employer had not cleared him to speak publicly, said the agency did have a degree of latitude in choosing which documents were subject to disclosure.

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“I honestly can't say that it was a conscious decision whether to include them or not,” the official said of the disclosures during the Bush and Obama administrations. "In particular with requests that deal with this topic, when you're talking about the records of individuals, there's some broad disagreement as to what is subject to release and what's not."

But transparency advocates were more concerned than they were convinced.

"This is something that you should expect," said Alex Howard, deputy director of the Sunlight Foundation. "If you don’t have very strong political signaling from the top that this is important, then you’re going to see the agencies take the foot off in terms of proactively disclosing and continuing to disclose as much as they were before."