A coalition of immigrant advocacy groups says authorities have begun deportation proceedings against an estimated 13,000 inmates held at Rikers Island since 2004.

The groups say they obtained the data through a Freedom of Information Act request and that it shows how the city's Department of Correction works with federal immigration authorities.

The DOC says it tells federal immigration officials about newly-admitted, foreign-born inmates but doesn't provide information about their immigration status.

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