Police said that last month they arrested seven people, including two midwives, for taking part in the alleged operation.
The Jakarta Globe said the suspects worked in a clinic in Jakarta and told poor mothers they would take the baby and give it a better future, bribing the mothers with money.
The group handled paperwork requirements, including identification cards and certificates from the clinic, the newspaper reported.
Police said they are investigating whether the group has ties internationally or if the babies were delivered directly to adopting mothers.
The group gave mothers between $720-$2,060 and paid medical costs, Jakarta Globe said.
Police said they believe the group has sold dozens of babies.