(CN) – Saying he is one of 4,000 federal prisoners being confined past sentence calculations, an Illinois man brought a federal complaint to secure his immediate release.

Robert Shipp filed the suit Friday in Washington with attorneys at New Civil Liberties Alliance. Though he was initially sentenced to life in prison on federal drug charges filed against him in 1993, Shipp later had his sentence reduced to 30 years, the remainder of which he has been serving out from home confinement in Chicago.

Thanks to good-time credits, Shipp says the Bureau of Prisons set May 6, 2019, as his new release date but “refuses to apply that calculation until July 19th, thereby keeping him confined for what will be 74 days beyond what BOP itself has calculated.”

July 19 is significant because that is the deadline for the bureau to release a risk and needs assessment instrument in connection to the First Step Act, a 2018 federal law that extended the amount of good-time credits prisoners receive for earning their GED or high school diploma from 47 to 54 days a year per year served.

“What they’re doing and what they told Robert is, we recalculated your release date – which has already passed – but we’re not going to actually give you the release date until the 19th because that’s the deadline we’ve set up for ourselves,” Shipp’s attorney Caleb Kruckenberg said in an interview.

“In some ways that’s an improvement but it’s still beyond what he’s supposed to serve,” Kruckenberg added.

Kruckenberg estimates there are somewhere between 3,000 and 4,000 prisoners like Shipp who are in custody right now, awaiting release dates like have already passed.

As for the July assessment, Kruckenberg says the process for determining criteria lacks transparency.

“The position right now is that once that instrument has been completed they will release people with good-time credits,” Kruckenberg said. “They believe that will be finished on July 19 but, given the way the BOP have dealt with this entire situation, I’m not overly optimistic they will follow that deadline.”

A representative for the Bureau of Prisons declined to comment on the suit, citing department policy on pending litigation.