https://fragdenstaat.de/blog/2023/06/22/fuer-diese-firmen-arbeiten-strafgefangene
Sorry, the article is German (deepl.com for translation). It's about a years long process to get information on which German companies benefit from prison labour - information which is legally accessible by the public. Not only did they have to place tons of freedom of information requests, but they also often had to sue to get the information released. There are a significant number of globally recognized companies on the list.
The organization FragDenStaat (Ask the State) is a bit sketchy as its funded by Pierre Omidyar, but critical support as they are bringing some important information into the public eye.
Here's what the German Interior Ministry had to say about the org in court:
More and more things reaching the public via portals like FragDenStaat. This is a development that's undesired by the management.
Durch Portale wie FragDenStaat gelangen immer mehr Dinge an die Öffentlichkeit. Das ist eine Entwicklung, die für die Verwaltung nicht wünschenswert ist.