A federal judge ordered the Boston Police Department and the Suffolk County District Attorney to notify their officers and prosecutors that people have the right to secretly record police, as long as the police are on-duty and in public.

Chief Judge Patti B. Saris’ declaratory judgment Wednesday serves to enforce a decision from last December, when she ruled it was unconstitutional for police to arrest people for secretly recording government officials.

Two of the plaintiffs in that case were René Pérez and Eric Martin, two Boston civil rights activists who secretly recorded the police on the Common and at Arizona BBQ in Roxbury. The Massachusetts ACLU’s Matt Segal represented Martin and said the case was brought on behalf of several people who were unlawfully arrested.

“We were finding that people were being arrested and being charged with secretly recording police officers who were performing their duties in public,” Segal said, “And we believed that those arrests and those prosecutions were improper and unconstitutional.”

According to the December court decision , since 2011, the DA’s office opened at least eleven case files involving a felony charge under Section 99, a state wiretap law from 1968. During the same period, the Boston Police arrested nine people for secretly recording police officers while doing their jobs in public.

Now Suffolk DA Rachael Rollins and the BPD have 30 days to tell their officers about the December ruling. In a statement sent to WGBH News, Rollins said her office will comply with the order and is discussing next steps with the Attorney General’s office. The Boston Police declined to comment.