American Airlines is in bankruptcy protection, but US Airways has been profitable in recent years
The US justice department has filed an anti-trust case seeking to block the merger of American Airlines and US Airways.
The deal, which would create the world's largest airline, was approved by a judge in March.
The complaint says customers would see a price rise as the merger would "substantially lessen competition" in the domestic market.
Six US states and the District of Columbia have joined the suit.
"By challenging this merger, the department of justice is saying that the American people deserve better," US Attorney General Eric Holder said in Tuesday's statement.
"This transaction would result in consumers paying the price - in higher airfares, higher fees and fewer choices."
The lawsuit also cites direct competition between the airlines on nonstop routes worth about $2bn (£1.3bn) in annual revenues.
American Airlines has been in bankruptcy protection since November 2011, but US Airways has been profitable in recent years.
The two combined airlines would have 6,700 daily flights and annual revenue of roughly $40bn.
Source: BBC News - Business http://www.bbc.co.uk/news/world-us-canada-23687680#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
_Free_Online.gif)
