Peter McParlin, chairman of the Prison Officers Association, has accused the Ministry of Justice (MoJ) of over-reacting to a violent jail incident involving Woolwich murder suspect Michael Adebolajo.
Five prison officers have been suspended following the apparent restraint of Adebolajo on Wednesday. All "strenuously deny" any wrongdoing.
Mr McParlin told BBC Radio 4's Today programme: "We have spoken to our members and on the basis of what our members have told us they have done absolutely nothing wrong. We are concerned that the Ministry of Justice have over-reacted due to the notoriety of this prisoner."
He also criticised the MoJ for failing to "correct false reporting" of the incident at Belmarsh.
More top news
The former royal marine could be released in as little as two weeks after his sentence was reduced from murder to manslaughter.
The painting of the late singer was auctioned to help raise funds for HIV and Aids prevention and awareness.
Katie Hopkins has accused JK Rowling of living in a "fantasy land" as the two clashed in the aftermath of the Westminster terror attack.