Immigrant advocates say authorities have begun deportation proceedings against an estimated 13,000 inmates held at the Rikers Island penal complex in New York City since 2004.

A coalition of immigrant advocacy groups** says they obtained the data through a Freedom of Information Act request. The data demonstrate how the city’s Department of Correction works with federal immigration authorities.

The groups plan to release their findings at a news conference Tuesday.

The Department of Correction says it gives information about newly-admitted foreign-born inmates to federal immigration officers but does not provide information about immigration status.

The Rikers policy predates a broader federal effort to identify and deport illegal immigrants in local jails.

** Including Make the Road New York