Thailand's securities regulator and stock exchange warned shareholders of solar power firm Superblock Pcl to scrutinise its planned $407 million investment in a solar power project after an independent financial adviser criticized the deal.

Such a warning from the regulators is relatively rare in Thailand, and while it does not impose any limits on the stock's trading, it brings the deal under critical focus. But the fate of the project, which requires approval of two-thirds of Superblock shareholders, was not clear.

Adviser Sage Capital had said two weeks ago that Superblock's proposal to acquire five solar power companies with combined capacity of 290 megawatts (MW) for 14.45 billion baht ($407.3 million) was flawed and that shareholders should not approve the investment in two of the five companies given that the fair value was lower than the acquisition prices.

"The SET recommends Superblock's shareholders to carefully study the IFA (independent financial adviser) report," the Stock Exchange of Thailand (SET) said in a statement. Thailand's Securities and Exchange Commission also issued a similarly-worded statement.

Shareholders will vote on the plans on Oct 30.

Sage Capital had also opined that a condition of the investment required Superblock to make a huge payment in advance to the counterparties, which was considered unfair and could lead to an opportunity cost on the funds prepaid.

Superblock's Chairman Jormsup Lochaya said the investment was suitable for the company's business and should help strengthen future revenue growth.

Superblock has said it was on track to achieve its target for commercial operation of 500 MW of capacity this year.

Suwintawong Gold Asset Company Ltd was the biggest shareholder in Superblock with a 21.2 percent stake as of end-August, according to Thomson Reuters data.

"Even though IFA has opinion against the plans, it does not mean the deals will collapse," said Sombat Akwanwattana, analyst at DBS Vickers Securities.