In the lawsuit, the shareholders asserted that Sirius XM directors failed to establish anti-takeover defenses for the U.S.-based satellite broadcaster despite efforts by Liberty Media Chairman John Malone to gain control of the company. Malone himself serves on the Sirius XM board due to Liberty Media’s current 48 percent stake in the company.

   “Liberty executives on Sirius XM Radio’s board are improperly preventing fellow directors from adopting anti-takeover provisions even if doing so would be in the best interests of the company and its shareholders,” the plaintiffs said in the filing.

   In July, Liberty Media Chairman Malone said he was planning to spin-off Sirius XM Radio into the largest satellite-radio company in the United States after Liberty Media received approval from the U.S. Federal Communications Commission (FCC) in May to assert control of Sirius XM.

   “If I’m in control, I like to have separate companies, run independently, with public shareholders investing in that business,” Malone said in a statement to investors and media. “There is no question eventually Sirius will be an independent company. The question is, in what time frame and in what circumstances?”

   Liberty’s investment in SiriusXM includes a $530 million load it issued to the broadcaster in 2009. Since then, Liberty raised its effective stake in SiriusXM to 46.2 percent and has told the SEC and FCC it intends to take over the satellite radio company by buying more shares. Liberty added its intention to nominate more people for election to the SiriusXM board to secure a majority. Though Liberty currently has five representatives on SiriusXM’s 13-member board, its FCC petition includes a reference to replacing the entire SiriusXM board after acquiring sufficient shares of stock.

   Separately, Sirius XM Radio announced that it recently passed 50 million factory vehicle installations of the company’s satellite radios. Sirius XM services will be factory installed in close to 70 percent of all new vehicles sold in the United States in 2012.

   “We are proud that SiriusXM has reached this major milestone since it directly reflects the strong commitment by all automakers to satellite radio and the high level of enjoyment by consumers for our unrivalled audio entertainment service,” Sirius XM President of Operations and Sales Jim Meyer said in a statement. “We expect to double factory installed vehicles to more than 100 million by 2018 and plan to offer our unique content and valuable entertainment to even more customers in the future.”