Complaints have been made to gardai after the 38-year-old allegedly made the threats while confronting staff, according to sources.
Prisoner Officers’ Association deputy general secretary Jim Mitchell said while such abuse was “unfortunately part and parcel” of the job it was “totally unacceptable.”
“The more serious they get the more serious we get. It’s not acceptable in any shape or form, but saying that doesn’t make it go away. ”
Penrose, who was recently convicted of murdering his pal Philip Finnegan in a brutal gang-related murder, has a record of bad behaviour behind bars.
Gardaí have previously investigated allegations that he exposed himself at female prison officers in an alleged incident in 2017.
Sources have described him as a highly disruptive prisoner who regularly threatens members of the staff.
While serving his sentence for the manslaughter of David Sharkey in 2010 he was regularly moved from prison to prison across the country while doing his time.
He is due back in court for sentence for the Finnegan murder at the Central Criminal Court on 13 December.
He has previously served seven years behind bars for the manslaughter of David Sharkey in 2010.
The son of a garda, Dubliner Penrose killed Finnegan in August 2016 in a horrifying attack in which he was abducted his friend, killed and attempts made to burn the decapitated body.
He was missing for over three weeks before his remains were found in a shallow grave in Rahin Woods, Co Kildare by a man out walking his dog
The Prison Service do not comment on individual cases but a spokesperson did say “any act of violence against a prison officer is unacceptable.”
Any criminal acts should be reported to the gardaí and it is “vitally important” staff are given support, it was added.
There is specific legislation relating to threats or assault on prison officers during the course of their duties which can be punished by up seven years in prison.
Figures show despite that assault of staff dropped considerably during 2020 from 123 in 2019 to 70 reported incidents.