Consumer advocate Ralph Nader said Liberty Media Corp Chairman John Malone's offer to buy out the remaining stake in satellite radio company Sirius XM was "ludicrous" and called for activist investor Carl Icahn to take notice.
Nader, a Sirius shareholder, said on Monday that Liberty's $3.68-a-share bid was below the $4 where the company was trading a few weeks ago.
Shares of Sirius climbed 6.5 percent to $3.80 in morning trading.
"I am sure that I along with other shareholders in Sirius XM will be interested in a legal challenge to John Malone's company for lowballing Sirius XM's shareholder value," Nader said in a statement.
"Carl Icahn - take notice and interest."
It was not immediately clear how many Sirius shares Nader owns. Nor was it clear whether Icahn is a shareholder of the company, although he is known to take an active role at corporations in which he owns stakes, such as Apple Inc.
A spokeswoman for Liberty Media did not immediately respond to a request for comment.
Liberty Media, which owns a majority stake in Sirius, launched a buyout offer to the company's minority shareholders on Friday.
The timing raised eyebrows since Liberty is also in pursuit of Time Warner Cable Inc. Taking full control of Sirius, which is expected to generate $1.5 billion in earnings before interest, taxes, depreciation and amortization this year, gives Liberty the financial flexibility for other deals, its executives said.
Liberty owns a large stake in cable company Charter Communications Inc.
Meanwhile, Sirius' rival online streaming music service, Pandora Media Inc, said the number of active listeners rose 13 percent to 76.2 million in December. Shares of Pandora rose almost 10 percent to $30.30.
(Reporting by Jennifer Saba in New York; Editing by Lisa Von Ahn)