Plans for a new wing at a young offenders' institution in Staffordshire would make it one of the largest in the country.
The Prison Service has submitted a planning application for the expansion at Swinfen Hall YOI near Lichfield which currently houses 320 offenders.
The proposed new wing would house 180 people.
The Prison Service said the wing is needed to ease the pressure of a rising population at the institution.
The proposals include plans for a three-storey block in the north west corner of the existing site
Lichfield District Council has already granted permission for plans to build another block at Swinfen Hall which will offer an extra 120 spaces.
A council spokeswoman said no objections had been received for the latest plans.