The cloverleaf-shaped building was constructed in 1975 and remained a part of Northwestern Memorial Hospital's operation until 2011.
The building is currently vacant, but several architectural groups say it's a mistake for the commission not to protect it.
"We believe prentice is worthy of protection and re-use because of its unique design- distinctive appearance and its infinite flexibility," said Chris Morris, National Trust for Historic Preservation.
Northwestern University officials have said they would like to raze the structure to build a new research facility on the site.
