In 1991 NASA was still designing its Freedom space station, and with the recent opening up of the Soviet Union NASA began to investigate using the Soyuz as a return vehicle for the station. Due to complications resulting from Orbital mechanics this would require flying the Soyuz spacecraft inside the Space Shuttle payload bay.

I have to give a lot of credit to David Portree who researched this in the past and made it easy for me to find the sources I needed. This is his original article from 2015:
https://spaceflighthistory.blogspot.c...
He also has a Patreon which is supporting him while he's between jobs, I'm a supporter because he's one of the best space historians out there :
https://www.patreon.com/user?u=168347

Here's a few other references for those who are interested:
https://ntrs.nasa.gov/archive/nasa/ca...
http://archive.gao.gov/t2pbat3/151975...
https://books.google.com/books?id=k05...