In the largest one-time release of federal prisoners, the U.S. Department of Justice has announced it will set free thousands of inmates by the end of the month.

The Federal Bureau of Prisons says it will release 35 inmates in Arizona, but it did not specify where those inmates are currently being held. The Bureau says more than 4,000 drug offenders will be released nationwide.

The release comes after the U.S. Sentencing Commission last year reduced the punishment for drug offenders and those changes were made retroactive. The release is part of an effort to reduce the nation’s incarcerated population, which currently stands at more than 2 million.

Congress is also debating a proposal to reform federal criminal sentencing laws.