Judges who send people to prison for less than a year should be forced to explain their reasons why.
The Irish Penal Reform Trust (IPRT) wants to see fewer jail sentences for less serious offences.
It says community service should be used instead but it is proving unpopular in the courts.
"This is not about influence or interfering with judicial discretion," said Fiona Ni Chinneide from the IPRT.
"This is about tracking the reasons why because our research has thrown up more questions than we could answer.
"It's absolutely essential that we know why judges are handing down short-term prison sentences in some cases and in some court jurisdiction to better inform policies."