The suit has been filed by lawyers Kreindler & Kreindler in Los Angeles, and alleges that the directors of Intermix, owner of MySpace.com, engineered the sale to News Corp so that it benefited themselves at the expense of public shareholders.
It says that the $12-a-share price offered for Intermix is "glaringly inadequate and unfair". It also says that the company's directors have not undertaken all the necessary steps to maximise stockholder value.
Kreindler & Kreindler's Gretchen Nelson described the actions of the Intermix board as "unconscionable".
"Our investigation has revealed that other prominent companies expressed interest in advancing more attractive acquisition proposals, only to be given the cold shoulder by the self-interested defendants," she said.
MySpace.com has seen growth of 400% over the past year, and in April it received more hits than Google.
News Corporation is buying Intermix as part of a $2bn internet spending spree. It is also reported to be interested in acquiring the search firm Blinkx and gaming company IGN Entertainment.
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