'Superman' Production Upsets Atlanta Prisoners Over Alleged Security Restrictions

Superman fans are super stoked the sequel to James Gunn's DC blockbuster has started production in Georgia ... but there's a group of people who ain't so happy ... local prisoners.

TMZ has learned from an inside source ... inmates at FCI Atlanta are pissed at the production because the "Man of Tomorrow" shoot is allegedly messing up their routines -- and more importantly, access inside the joint. Basically, while the flick is in production, we're told prisoners have to remain in their cells way more than under normal circumstances -- and even worse ... no access to commissary.

A spokesperson for the Federal Bureau of Prisons tells TMZ ... they'd never comment on internal security practices or procedures in general ... but if a warden did put a facility on modified operations status, it would be for the safety of staff and inmates. Usually, such an order would happen after a violent incident that needed to be investigated.

Another source with direct knowledge tells TMZ ... production is shooting in a small section of the facility ... and they should be wrapping on the location soon.

"Superman" writer-director Gunn shared a picture from the prison on Monday ... showing it's where Nicholas Hoult's Lex Luthor ended up after the previous flick ... thereby confirming "Man of Tomorrow" started shooting.

As for the modified operations status ... IF it is happening at the Atlanta slammer, we're told all inmates still have daily access to at least three meals per day, potable water, and medical and psychological services.