Robert Shipp is serving the remainder of a federal prison sentence on an ankle monitor in Chicago, Illinois. But Shipp is being held unlawfully by the U.S. Bureau of Prisons.

Even though he was due to be released from custody last month under a change in federal law, the BOP has refused to release him while it waits until July 19, 2019 to apply the new law at its discretion. There are some 4,000 federal prisoners like Shipp across the country who sit in limbo at BOP’s mercy.

Congress eliminated parole for federal prisoners in 1984, and ever since, a person must serve the full term of imprisonment to which he has been sentenced. The only credit one may receive toward that sentence is “up to 54 days at the end of each year of the prisoner’s term of imprisonment” for good behavior. This language may appear to mean that someone would be able to receive 54 days off of his sentence every year, but the BOP actually uses a calculation methodology that grants good time only for time spent in prison, as opposed to the duration of the sentence imposed by the court. This difference results in about 47 days off a sentence every year, or about a week less than what Congress intended. While seven days per year may not seem like much time to give up, these weeks add up over the course of yearslong sentences.

On Dec. 21, 2018, as a part of the First Step Act of 2019, Congress finally fixed this accounting problem and ordered BOP to give prisoners the full 54 days of good time credit they earn for good behavior every year. Congress expected this bipartisan fix to take effect immediately.

When the First Step Act was passed, an estimated 4,000 people became eligible for release from custody under the good time fix. But they weren’t released.

Shipp is one of those people. Originally sentenced in 1993 to a mandatory life term in prison for selling drugs, Shipp’s time in BOP custody was reduced to 30 years thanks to retroactive criminal justice reform legislation. With good time credit, he had been set for release on Nov. 26, 2019.

When the First Step Act passed in December, Shipp’s release date should have been recalculated to March 26, 2019. But that release date came and went, and the BOP continued to hold him in custody. This month, the BOP finally informed Shipp that even though it has already calculated his release date (as May 6, 2019) and agrees that his release date is in the past, he is not scheduled to be released until July 19, 2019. According to the agency, the First Step Act doesn’t actually take effect until then. The BOP has, yet again, come up with a creative loophole to avoid its legal responsibilities and keep people in custody longer.

Each day the BOP ignores Congress’ orders, thousands of people continue to be held beyond their lawful release dates, away from their families. BOP is stealing time from them that they will never get back. Agencies like the BOP cannot wait until they find it convenient to follow the law; they should uphold the law and give people the good time credit they have earned.

Caleb Kruckenberg is litigation counsel at the New Civil Liberties Alliance, which recently filed a complaint against the BOP and requested an emergency court order forcing the agency to comply with the law as written.