Dell's largest independent shareholder is teaming with activist investor Carl Icahn in another challenge to founder Michael Dell's $24.4 billion bid to take the struggling computer maker private.

Southeastern Asset Management and Icahn say they will offer shareholders $12 per share in cash or additional stock in a deal that keeps Dell Inc. publicly traded. They say this gives shareholders a stake in future gains made by the Round Rock, Texas, company.

An investment group led by Michael Dell is offering $13.65 per share in a deal that would take the company private. Southeastern and Icahn criticize that proposal in a scathing letter to Dell's board outlining their proposal.

Icahn also has made a preliminary proposal to buy 58 percent of Dell stock for $15 per share.