Hossein Ronaghi was arrested in December 2009 during the crackdown following mass protests against that summer's presidential election. He was later sentenced to 15 years in jail and is currently in Tehran's Evin prison.
Relatives say Ronaghi developed severe kidney problems while in detention but refused to undergo surgery in prison.
He requested that his family be present during the surgery and asked for leave to get the operation done outside prison.
But one of Ronaghi’s close relatives, who wished to remain anonymous for security reasons, told Radio Farda on February 2 that Evin authorities had denied Ronaghi temporary leave.
"Despite meeting several times with the authorities during my visit to Tehran, I was unable to convince them to grant Ronaghi leave for surgery," he said.
"His need for surgery is indispensable and the chance that one of his kidneys might fail permanently increases by the second. He might need surgery to remove his kidney. They are wasting vital time," he added.
The relative also said Ronaghi's immediate family has been allowed to visit him this week but that his lawyer has been banned from seeing him in prison, "which is a basic right of any prisoner."