The Financial Times and The Verge reported moderators for Facebook and YouTube, hired by the contractor Accenture, were sent the documents.
Moderators monitor objectionable materials and often view hundreds of disturbing images in a day’s work.
Accenture said the wellbeing of workers was a “top priority”.
In a statement the company added only new joiners were being asked to sign the forms, whereas existing employees were being sent the form as an update.
“We regularly update the information we give our people to ensure that they have a clear understanding of the work they do,” Accenture said in a statement.
Accenture is a professional services company hired by firms including Google, Facebook and Twitter. Its contractors work as outside monitors for social media sites to remove any inappropriate content. The job often requires watching and listening to disturbing posts that can be violent or sexual in nature.
Both The Verge and Financial Times report that moderators were sent documents that required to them to acknowledge the mental health risks of the role.