Part of the letter included what has been described as a "call to arms".
After the letter was posted on the internet this week, Corrections chief executive Christine Stevenson said the accused would be blocked from sending or receiving mail pending a review.
The accused gunman's lawyer, Shane Tait, today declined to comment on the prison letters, saying he would need to seek instructions from his client.
Survivor Nour Tavis told the Herald he was angry and upset to hear about the prison letters.
"I think it's not a good idea that he can send them, he's going to spread hatred," he said.
"The words might appear like they are innocent but they are dangerous - they could have codes... people like him could be reading between the line, there could be a message.
"I call him a contaminant and what he is doing is contaminating others."
Tavis scrambled out a smashed window when a gunman burst into the Al Noor Mosque on Deans Ave and opened fire.
He saw many of his fellow worshippers fall around him as they tried to escape but were struck by bullets.
Tavis said he still suffered nightmares about March 15 and was triggered by other shooting or violent incidents that happened around the world.
He believed that people with the same beliefs as the accused would be spurred on by his letters.
"He's inspiring other people and that is a big no-no to me," said Tavis.
"He is a human being, he must have his rights, but within limits - I don't want him to harm anymore people.
"Directly or indirectly, we are all affected by these things.
"Some of my friends lost the only person they had in the world to provide for them, it's really tough.
"Now irresponsible people could see a message from [the accused], read between the lines, and do other things."
Tavis said the accused should be able to have contact with his own family, but that was it.
"We should not have to hear this... we are just starting to forget things and it comes back up - it's not fair," he said.
"I am against him sending any more letters."