There’s really not much English-language information about this situation available at the moment, but according to the Bulgarian Prisoners’ Association:

“There is a mass strike by over 60 prisoner workers in Sofia Prison in protest over the order for slave labour by the National prison Director Svilen Tsvetanov as he has ordered prisoners to work 4 times more then is physically possible.”

For updates and more information on the situation as it develops, keep an eye on the Bulgarian Prisoners’ Association fb page. To help support the work of the Bulgarian Prisoners’ Association, you can donate via paypal to contact@bpra.info or by using the “donate” button on their website. (If you’re wondering about why there’s an “r” in there, it’s because they can’t seem to make up their minds about whether they want “rehabilitation” in their name or not.)