With sporting events cancelled around the globe due to the novel coronavirus outbreak, the UFC is staging three cards in eight days in Jacksonville, Florida.
Before competing, fighters taking part in the UFC 249 event on May 9 were asked to sign an eight-page event participation agreement.
A non-disparagement clause in the undated agreement states that "the Participant will not suggest or communicate to any person or entity" that the events "have been or will be held without appropriate health, safety or other precautions, whether relating to COVID-19 or otherwise."
The agreement goes on to say that if a fighter does breach this clause, "the Company may revoke all or any part of any prize monies or awards won ... including, but not limited to, purses, win bonuses, other fight-related bonuses and event-based merchandise royalties."
Though signed exclusively to the promotion, UFC fighters are independent contractors rather than employees, and purses and bonuses form a major part of the income of almost all of the fighters on the roster.
A UFC spokesperson declined to comment on the clause and the possibility of penalties being imposed on fighters, instead referring to comments Dana White gave to Yahoo in which the UFC president said that fighters would not be punished for airing their opinions about the health and safety arrangements.
"If a fighter says something that isn't true — if he says we didn't test anyone for this — that would (violate the agreement). But if he said something that was true, his opinion, then that is different," White said.
In recent weeks, one fighter has expressed reservations about getting in the cage during the COVID-19 pandemic.
Heavyweight Greg Hardy, who suffers from asthma, said in a news conference on Thursday that he was "terrified" of the virus, but he went on to compete on the UFC 249 card and scored a decision victory over Yorgan De Castro.
A planned middleweight bout between Ronaldo "Jacare" Souza and Uriah Hall on Saturday was called off after Souza tested positive for COVID-19 following his arrival in Florida.