The merger will have to be approved by the FTC, Federal Trade Commission, I believe. As mentioned earlier in the thread, they will claim their competitors are terrestrial and internet radio stations, not each other. To a certain extent they have a pretty strong argument. Say each one has 5% of the total market, together 10%. Are they trying to steal customers from the other guy's 5% or from the 90% of other folks out there?
EDIT: From hearing additional news stories about this, a key regulator is the FCC, or Federal Communications Commission, which has a rule that basically bars monopolies from satellite radio. This is considered the top hurdle to overcome in the contemplated merger.
It is however, bad news. I could easily see them cutting services and raising prices. At least I just renewed for 2 years, and I think they have a long term deal with MLB, so okay for a while. It would be okay if they consolidated similar music formats, they could have some economies there without impacting the product much.