State-owned energy giant China Three Gorges (CTG) is facing a surprise roadblock in its hopes to acquire Portuguese utility Energias de Portugal (EDP).

Activist investor U.K. fund Elliot Advisors, one of Energias de Portugal’s (EDP) major shareholders, released a letter on Thursday calling for “an alternative, more promising pathway” to replace CTG’s bid.

The company said it believes “EDP possesses a collection of high-quality yet undervalued assets, with substantial unrealized potential,” but added that “CTG’s bid, if consummated, will leave the company weaker, more volatile, and with a less attractive portfolio and diminished growth opportunities.”

CTG is already EDP’s largest shareholder, with a 23% stake. In May, it offered to take over EDP with 9 billion euro ($10.7 billion) — but EDP rejected the initial price as too low. The current status of the deal has not been disclosed.

CTG told Caixin that the company is unaware of the issues raised in Elliot’s letter. 

Related: Quick Take: EDP Rejects Takeover Offer From China Three Gorges