Connecticut Attorney General William Tong had previously said he was considering an appeal, in a judge's approval of Stamford-based Purdue Pharma's bankruptcy plan.
Now, Tong's office has filed a notice of appeal.
Tong objects to provisions in the bankruptcy plan that give the company's owners, members of the Sackler family, protection from lawsuits by opioid abuse victims.
"The Sacklers are not bankrupt. We cannot allow our bankruptcy laws to be abused and misused as a loophole for the rich and powerful to avoid justice and accountability, Tong said in a statement. "This decision was an unprecedented and unacceptable overreach by the bankruptcy court."
The federal Justice Department also appealed the judge's approval.
The Sacklers will pay $4.3-billion, but Tong says that is not enough.
The Sacklers say they acted legally in running the company.
Purdue's efforts to downplay addiction risks and boost sales of Oxycontin resulted in federal criminal prosecutions of the company.
Oxycontin played a key role in a wave of addiction across that country that resulted in a surge of overdose deaths.
