The Seoul Central District Prosecutors' Office has begun investigating former Supreme Court Justice Kwon Soon-il over suspicions he had served as advisor to an asset management company at the center of a favoritism scandal without registering as a lawyer.

The Supreme Prosecutors' Office said Friday it assigned the case to the Seoul branch after a complaint was filed against the former judge on charges of violating the Attorney-at-law Act.

Kwon allegedly received a monthly salary of 15 million won for his service as an advisor to Hwacheon Daeyu after retiring as a justice last September.

If it is found that he offered legal counsel at the firm, some say that could be a violation of related law, as he was not registered as a lawyer.

Since the dispute emerged, Kwon said he accepted the position after checking whether the stint would go against the public officials ethics law and anti-graft law.

Hwacheon Daeyu is implicated in the latest scandal involving alleged business favors in a development project in Seongnam City that took place when presidential hopeful Lee Jae-myung was mayor.