The message, reported by Variety, warned that "not only you but your family will be in danger."
Sony's computer system was attacked in late November and gigabytes of data, including unreleased movies, were stolen and leaked online. Embarrassing hacks have hit other companies in recent years, but threatening employees is highly unusual and will put extra pressure on law enforcement to find those responsible.
The message purports to be from the Guardians of Peace, the group that has claimed responsibility for the Sony hack. It's written in patchy English and opens with further threats against Sony.
"Removing Sony Pictures on earth is a very tiny work for our group which is a worldwide organization. And what we have done so far is only a small part of our further plan," the message reads in part, according to Variety, which says it obtained a copy.
It then turns to Sony employees.
"Many things beyond imagination will happen at many places of the world. ... Please sign your name to object the false of the company at the email address below if you dont want to suffer damage. If you dont, not only you but your family will be in danger," the message reads.
It wasn't immediately possible to confirm the authenticity of the message and Sony Pictures couldn't be reached.
An email to an address that claimed earlier this week to be "the boss of the GOP" was returned with the error message "User account deactivated."
Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com