Indonesia's highest court is expected to decide soon on whether the Financial Services Authority (OJK) has the right to supervise the banking industry, a plaintiff said, a responsibility it obtained from the central bank a year ago.

The Constitutional Court is reviewing a legal challenge brought last year saying OJK's authority overlaps with the mandate of Bank Indonesia.

"The supervision of the banking industry cannot be separated from monetary policy or it would become unclear who is in charge of monetary stability," said Salamuddin Daeng, one of the plaintiffs.

Daeng, who is a researcher at pro-trade NGO Indonesia for Global Justice, wants the supervision of the banking industry to return to the central bank and OJK either be scrapped or placed under the control of the finance ministry.

The court could not be immediately contacted, while a central bank spokesman declined to comment.

The OJK took over as the financial sector regulator in Southeast Asia's largest economy in 2013, and took over as bank supervisor a year later.

OJK said it has not had enough time to prove itself as a regulator.

"We have paid too big of a cost to build OJK. We should try OJK first with its integrated financial supervision," Mulya Siregar, OJK's deputy commissioner for banking supervision told Reuters, adding that coordinating with the central bank has not been easy.

OJK's chairman and many of its commissioners and banking supervisors are former central bank officials.

But the two regulators do not always agree. A senior central bank official told Reuters last year he thought some of OJK's approach for banking rules were old-fashioned.