A prison officer at HMP Lancaster Farms says he was given a sickness warning when he returned to work after being treated for cancer.
The Prison Officers Association (POA) has stepped in to support the unnamed officer, in his 50s, after hearing his absence triggered disciplinary procedures.
Mark Fairhurst, POA national chairman, said: "We reached an agreement in 2017 that they can use empathy and discretion."
The POA is calling for the warning to be rescinded on the grounds it is in breach of the Equality Act.
Mr Fairhurst said: "If the officer has a warning on his record and he needs further treatment for prostate cancer or ends up in a bad way, he will be fearful of going off sick.
"He could end up on half pay or even worse, losing his job."
In 2017 the POA issued guidance to prison governors relating to attendance management and disability discrimination.
Mr Fairhurst said: “It’s clear this particular manager does not understand the Disability Discrimination Act and has failed to read the guidance document we agreed.
"Besides that I would expect staff in this position to be treated like human beings and not just a process to be applied. I fully expect to receive a call informing me the warning has been rescinded and common sense has prevailed. That is the only resolution we will accept.”
The Ministry of Justice has been approached for comment.
