A proposal that could change the way past drug crimes are factored into new prison sentences is drawing opposition from some law enforcement groups and prosecutors.

A Minnesota law that took effect in August instituted milder penalties for some drug crimes. The current proposal would use those milder new standards when factoring an offender’s criminal history into the sentence for a new offense. Supporters of the proposal say it’s a necessary tool to reduce racial sentencing disparities in the state.

County prosecutors in the state say they’re worried the modification could mean that some violent offenders will receive lesser sentences. Robert Small, executive director of the Minnesota County Attorneys Association, said the issue of whether to categorize drug crimes in an offender’s criminal history under the new or the older standards was already decided by the Legislature.

“Retroactivity was an issue as the bill was making its way through both the Senate and the House, and it was clear in the passage of the bill that it would not be retroactive,” Small said. “From the county attorneys’ perspective, this is an attempt to make something retroactive that the Legislature decided would not be retroactive.”

Small said he believes the proposal could lead to shorter sentences for repeat violent offenders.

But failing to make the change would lead to more people in prison for longer sentences, said Lars Negstad, strategic campaigns coordinator for the faith-based group Isaiah.

“The legislative attempt was clearly to recognize that we’re locking up too many people who are suffering from drug addiction,” Negstad said. “Now, unfortunately, the county attorneys’ association is pushing this application of the rule that basically would lock people into the harsher, old guidelines, rather than apply the new guidelines.”

Negstad said using the older standards to calculate sentences would reinforce racial disparities in sentencing and undermine the law passed by the Legislature to reduce penalties.

The law “was really a modest step in the right direction. It didn’t even go far enough,” Negstad said. “Now to move in the opposite direction would be just a gross injustice.”

The Minnesota Sentencing Guidelines Commission took comments on the proposal at a hearing this week and is expected to vote Dec. 30. If the proposal wins approval, it will be presented to the Legislature next month and could take effect in August.

Meanwhile, two Republican state representatives who object to the proposed change said they will move to limit the sentencing commission’s authority to make law.

Tony Cornish of Vernon Center and Brian Johnson of Cambridge announced Thursday that they want to eliminate a provision that enables the commission’s recommendations to become law unless the Legislature intervenes.

“The commission is once again attempting to circumvent the legislative process and is exceeding its statutory authority,” Johnson said in a statement. “Many in the Legislature are concerned about the direction this commission is going and this bill will address those concerns.”

“The commission seems to think the Legislature is merely a rubber stamp for its objectives rather than a branch of government that’s given the constitutional authority to create laws,” Cornish said.