What a lousy morning in Tempe and Ft. Worth. In an announcement today, the US Department of Justice filed a civil antitrust lawsuit to block the merger of US Airways and American Airlines.

“The merger of these two important competitors will just make things worse –- exacerbating current airline industry trends toward reduced service, increasing fares and increasing passenger fees."
There was no immediate response from the airlines, but the news must come as a shock. Just this week they let slip that US Airways was moving into AA's terminal at JFK next month. The official website for the merger anticipated the union starting as soon as the end of this month.
The government is concerned that the two airlines fly overlapping routes on more than 1,000 routes. A half-dozen state attorneys general joined the DOJ lawsuit, filed in a federal court in Washington, DC.
Perhaps the officials weren't happy by what it saw result from the last two mega mergers of United and Continental and Delta and Northwest.
Underscoring how perceptions as played out in media are vital:

"The department’s complaint states that executives of both airlines have repeatedly said that they do not need the merger to succeed."
See the DOJ announcement, here.