The large investment firm T. Rowe Price said Tuesday it was opposing Dell's proposed $24.4 billion private equity buyout, saying the offer "does not reflect the value" of the tech giant.
T. Rowe Price, which holds a 4.4 percent stake in Dell, joined the opposition from Southeastern Asset Management, which claims 8.5 percent of Dell shares.
"We believe the proposed buyout does not reflect the value of Dell and we do not intend to support the offer as put forward," T. Rowe Price chairman Brian Rogers said in a statement.
The news cast fresh doubt on the plan to go private in a deal that would give founder Michael Dell a chance to reshape the former number one PC maker away from the spotlight of Wall Street.
The plan, announced last week, is backed by equity investment firm Silver Lake and would include a $2 billion loan from Microsoft.
Dell brushed aside criticism Monday, saying the plan was "in the best interests of stockholders."
It said a special committee of its board considered "an array of strategic alternatives" and had "retained a prominent management consultant to help it assess the company's strategic position."
Dell's plan would give shareholders $13.65 per share in cash -- a 25 percent premium over Dell's closing share price on January 11, before reports of the deal circulated.
The move would delist the company from stock markets and could ease some pressure on Dell, which is cash-rich but has seen profits slump as it tries to reduce dependence on the shrinking market for personal computers.
Dell shares rose modestly Tuesday by 0.8 percent to $13.81.
A research note by Jefferies said an agreement is likely to stand around $15 per share.
"We believe that the bid could be raised to $15 to satisfy agitated shareholders," said Jefferies analyst Peter Misek.
"While many shareholders would obviously like a higher bid, we see competing offers as unlikely."
Misek said anything over $20 per share would make the profit potential lower for the buyout partners and that "Silver Lake and Michael Dell would walk away at those levels."