Heads of conglomerates and their family members have more than doubled their stakes after converting their ownership structure into holding companies.

The Fair Trade Commission(FTC) said Tuesday that out of 19 holding firms it analyzed, 12 involved the founding family members exchanging their affiliate shares with holding company shares.

This process had helped the conglomerate heads and their family members expand their stakes to 28-point-two percent and 44-point-eight percent, respectively.

The antitrust watchdog called for a systematic revision, saying efforts to resolve conglomerates' cross-shareholding arrangements among affiliates have further strengthened the founding family's control over them.

Conglomerates' holding companies are also heavily reliant on intra-group trading, and have expanded their presence in so-called second and third-tier subsidiaries in their multiple levels of affiliates.