Inmates currently must save for their own televisions, but the Corrections Department said the policy complicated cell searches for drugs and other contraband.
Opposition correctional services spokesman Terry Stephens says massive budget cuts in other areas meant the Government had its funding priorities wrong.
"This has always been an issue for prisoners. They must save for their own television sets," he said.
"We see no reason to change that and again, at a time when Keith Hospital can't keep its doors open because the Government can't find less than a million dollars to keep doors open, they can find money for flat screen televisions."
Public Service Association spokesman Peter Christopher has taken issue with the timing of the change.
"I've spoken to a number of correctional officers today and it would be fair to say it went down like a lead balloon," he said.
"Their immediate comment was 'we're having our long service leave and other conditions cut and the Government is spending money this way'.
"It'd be fair to say they weren't happy."
Correctional Services Minister Tom Koutsantonis says the plasma televisions will not be free for prisoners and will make cell searches easier.
"All South Australian prisoners from year dot since TVs have been broadcast have had TVs in our prisons," he said.
"A policy change would be taking TVs out of our prisons.
"They will still be charged a fee for the TVs but this will mean we'll own the TVs so if prisoners don't behave, we can take it away from them."