Two of Dell’s largest shareholders have made a new takeover bid for the struggling computer company that will challenge a previous offer from Silverlake and Michael Dell. Activist investor Carl Ichan and Southeastern Asset Management on Friday announced a new plan that would give current Dell shareholders the option keep their stock and receive either $12 per share in cash or $12 in additional shares valued at $1.65 per share. The offer counters a $24.4 billion bid led by Dell founder Michael Dell and private equity firm Silver Lake Partners to take the company private. Icahn and Southeastern hold a combined 13% stake in the company, compared to the 16% controlled by Dell and Silver Lake.

“It is insulting to shareholders’ intelligence for the board to tell them that this board only has the best interests of shareholders at heart, and then accept Michael Dell’s offer to purchase the company he founded for $13.65 per share, a price far below what we consider its value to be,” Icahn and Southeastern’s president G. Staley Cates wrote in a letter to the board of directors, according to Bloomberg.

Shares of Dell have continued to rise this year as buyout talks have made shareholders feel optimistic about the company’s future. The stock has gained more than 31% in the past five months and now trades around $13.40 per share, making Dell’s offer of $13.65 per share less appealing.

“Either give shareholders the real choice they are entitled to or face the legal liability for your failures,” Icahn and Southeastern said.