Under the current scheme in Scotland, long-term prisoners – those serving four years or more – become eligible for parole halfway through their prison sentence.
If they don’t get parole, they are freed automatically when they have six months left to serve.
The Scottish government wants to change the automatic release point to two-thirds of the sentence.
This would apply to all long-term prisoners, including people convicted of unlawful killing, rape, child abuse, drug trafficking, and attempted murder.
The proposals are complex, but if they were backed by parliament at least 630 prisoners would be freed straight away.
Another proposal would change the designation for short-term prisoners to those serving under five years.
Groups representing victims of crime have called for exemptions for sex offenders and people convicted of domestic abuse.
Excluding those offenders would reduce the impact of the proposed change.
Ministers will have to decide whether to press ahead regardless of the controversy, or scale down what they hope to achieve.
First Minister John Swinney has said some valid points have been made about exemptions, which could signal a possible change of heart from him.