Lotte Group Chairman Shin Dong-bin faced another leadership challenge from his older brother, who escalated the power struggle atop the Korean-Japanese retail conglomerate by launching a campaign to oust a key unit's board.

Shin Dong-joo, who was stripped of executive positions at the group last year after a failed coup attempt, called for all of Japan-based Lotte Holdings Co.'s board directors to quit, except his 93-year-old father — founder Shin Kyuk-ho— and for the company to hold an extraordinary general meeting, according to a statement in Tokyo.

Since the feud at the family-run group erupted into the public view last year, the disgruntled brother has criticized and thrown lawsuits at Lotte management, while the group has defended its current chief's legitimacy. The case has gripped South Korea, where such struggles at corporate dynasties — known locally as chaebol — are rarely displayed in public.

Though Lotte has operations in Japan, the group generates the bulk of its business in South Korea, where it has more than 80 affiliates in areas ranging from department stores to amusements parks and hotels with over 100 trillion won ($83 billion) of assets. Lotte Holdings is a particularly important unit because of its stakes in key affiliates and its role in coordinating group strategy.

Yet Lotte Holdings counts closely held Kwang Yoon Sa, which Shin Dong-joo says is 50 percent owned by him, as its biggest shareholder with a 28 percent stake.