Shares in both satellite firms have fallen as growth has slowed, and neither firm has managed to turn a net profit.
Regulatory issues
Blair Levin, an analyst with Stifel Nicolaus and former Federal Communications Chairman (FCC) chief of staff, said he thought the Justice Department and the FCC would give the deal the go-ahead, although he said it would be a "close call".
The National Association of Broadcasters, which acts for local broadcast stations, said the proposed alliance would create an over-concentrated market.
However, the two firms argue the deal should be allowed because they already face competition from all audio devices available - from car radios to digital music players.
The stations called the deal a "merger of equals" though Sirius would hold 53% of the combined firm's shares.
April Horace, an analyst with Janco Partners said: "I worry that both companies will be more focused on regulatory issues than they will be on the consumer."
