The legislation doesn't take away pension eligibility. The prisoner is still eligible; it's just a matter of suspension during the time period the prisoner is incarcerated, and the door is open when the prisoner is released to have his or her pension benefits restarted.
It's the same thing in terms of eligibility during the time they are incarcerated. They can apply; they just won't receive them until they're released.
So it's completely within the pension system, and it's a measure that's designed to be within the pension system.