An influential proxy adviser joined Elliott Management Corp. in opposing an $8.8 billion deal between two Hyundai Motor Group units, complicating the automotive giant’s ability to get shareholders to vote for an overhaul that may help the chairman pass control of the South Korean conglomerate to his son.

Glass Lewis & Co., which provides voting advice for more than 1,300 institutional clients, recommended that Hyundai Mobis Co. investors cast ballots against the “profoundly unattractive” plan, which calls for the company to sell some of its businesses to affiliate Hyundai Glovis Co. The deal undervalues the assets being sold, lacks business logic and seems designed to benefit Hyundai’s founding family, the proxy adviser said in a report on Monday.

The criticism is a setback for Hyundai’s Chung family as it prepares for Korea’s biggest proxy fight since Samsung Group narrowly defeated billionaire Paul Singer’s Elliott by muscling through a controversial merger of two units nearly three years ago. Should the Hyundai deal, which requires a two-thirds majority to pass in a vote scheduled on May 29, be blocked it would mark a landmark victory for foreign activist investors in a country where all such campaigns have failed.

Though Samsung beat Elliott in 2015, allowing the chairman’s son to solidify his grip on the group, it came at a cost as the heir-apparent to the business empire and the country’s president were jailed for corruption linked to the merger. Elliott is seeking $670 million in compensation from the Korean government for inappropriately meddling in that deal.

Hyundai Mobis shares fell 0.6 percent to close at 238,500 won, while Glovis dropped 3.8 percent, the most since May 4. Shares of Hyundai Motor Co., the largest company in the group, fell 1.7 percent.

Institutional Shareholder Services Inc., another major proxy adviser, has yet to come out with its recommendations. Along with Glass Lewis, it may be crucial to the Hyundai deal’s outcome, as neither the Chungs nor Elliott have the votes to determine the outcome. Foreign investors’ holdings in Hyundai Mobis exceeded 45 percent—more than enough to block the deal—as of April, according to data compiled by Bloomberg.

Hyundai, a sprawling group of 56 companies with more than $200 billion in assets, said it would continue its efforts to communicate with investors about the merits of the transaction.

“We believe our proposed restructuring plan is the optimal solution to secure future competitiveness as well as resolve regulatory issues for the entire group,” Hyundai Motor Group said in a statement after Glass Lewis’ announcement. “We will continue to communicate the benefits of our plans with all of the stakeholders.”

Hyundai Motor’s heir apparent, Vice Chairman Euisun Chung, spoke with Bloomberg in an unprecedented interview last week, whereby he acknowledged Mobis needs to do more to win over shareholders.

Elliott, which owns more than $1 billion stake in three Hyundai units—Hyundai Motor, Mobis and Kia Motors Corp.—has opposed the restructuring plan, saying it shortchanges shareholders. Instead of spinning off divisions of a group of suppliers and merging them with its logistics arm, the U.S. fund has proposed that Hyundai Motor Co. merge with Mobis to form a holding company that would oversee the group.

Elliott has also urged Hyundai to return more than 12 trillion won ($11.2 billion) in cash to shareholders.