MSD Capital is NorthStar Asset Management Group’s largest shareholder, and is the latest investor to voice concerns regarding the proposed three-way merger between NorthStar Asset Management, Colony Capital and NorthStar Realty Finance Corp.

The merger would form a new REIT called Colony NorthStar, which would have roughly $58B in assets under management. MSD—which owns 10.2% of NorthStar Asset—wrote in a letter earlier this week that the proposed merger doesn’t add enough value for investors, and raised concerns regarding the governance structure. The company added to activist pressure already voiced by Jonathan Litt of Land & Buildings Investment Management and Abrams Capital Management—NorthStar Asset’s third-largest shareholder.

Once the all-stock deal is finalized, shareholders from each company will own 33% to 34% of the new REIT, which was announced in June. Shareholder reaction to the proposed transaction remains mixed, Bloomberg reports, but analysts say more transparency could improve chances of the deal going through. [Bloomberg]