In a statement, Nader, a Sirius shareholder, said Liberty Media Chairman John Malone's $3.68-a-share offer was below the $4 where the company was trading a few weeks ago. Nader callied the bid "ludicrous." Liberty currently has a 52-percent stake in Sirius, but would take full ownership in the potential deal.
"Carl Icahn—take notice and interest," Nader said in his statement.
Icahn has not responded to Nader's comments. Last week, Icahn purchased 30 million to 40 million shares of car rental business Hertz, according to sources.
(Read more: Icahn takes stake in Hertz: Sources)