Diddy is facing new criminal charges in his federal case in New York ... because federal prosecutors just hit him with their third superseding indictment.

According to new legal docs, obtained by TMZ, the feds are tacking on two additional charges ... one for sex trafficking by force, fraud or coercion and another for transportation to engage in prostitution.

The feds say the new charges stem from allegations against Diddy from 2021 to 2024 and relate to an individual the feds simply refer to as "Victim-2."

Diddy's legal team has previously described the alleged victims in the case as former girlfriends ... and they've already essentially referred to Victim-1 as being Cassie.

With the new indictment, Diddy is now facing 5 criminal charges ... two counts of sex trafficking, two counts of transportation to engage in prostitution and one count of racketeering.

Diddy pleaded not guilty to the feds' previous indictments and his trial is scheduled to start May 5.

We reached out to Diddy's camp ... so far no word back.