The US justice department has filed an anti-trust case to block the merger of American Airlines and US Airways.

The complaint says customers would see a price rise as the merger would "substantially lessen competition" in the domestic market, the BBC informs.

Texas, Arizona, Florida, Pennsylvania, Tennessee, Virginia and the District of Columbia have joined the legal action.

"By challenging this merger, the department of justice is saying that the American people deserve better," US Attorney General Eric Holder said in a statement Tuesday.

"This transaction would result in consumers paying the price - in higher air fares, higher fees and fewer choices."

The USD 11 B merger, announced in February, took American out of bankruptcy, New York Times reminds. The combination of the two carriers would create the nation’s biggest airline, a company with the size and breadth to compete against United Airlines and Delta Air Lines, which have grown through mergers of their own in recent years and are currently the biggest domestic carriers.

The deal was approved by a federal judge in March and has been backed by the European Union, according to the BBC.