American Airlines and US Airways are dealing with a curveball handed to them late in the game on their road to creating the world’s largest airline.

The U.S. Justice Department filed an anti-trust lawsuit on Tuesday morning to block the tie-up. The filing says the merger would decrease competition and increase airfares for consumers.

We’ve covered the story closely since the first whisperings of a merger and chronicled the February 14 merger announcement on our liveblog.

The ten most important moments, in what was hoped to be a seamless merger, are outlined below:

» U.S. Justice Dept Files Anti-Trust Lawsuit To Block American-US Airways Merger
» EU Clears Way for US Airways and American Air Merger, With Conditions
» American Airlines Creditors Voting in Favor of Reorganization Plan
» US Airways shareholders approve merger with American Airlines
» AA-US Air merger causes regulatory concern with reduced competition on 1,600 routes
» Leadership team of new American Airlines gets heavy US Airways stamp
» American files bankruptcy exit plan, as it closes on US Airways merger
» AA-US merger gets court approval, decision delayed on Horton’s $20 million package
» How Doug Parker beat out Tom Horton for CEO
» It’s officially official: American and US Airways merge to create world’s largest airline

Photo Credit: An American Airlines plane (C) is seen between two US Airways Express planes at the Ronald Reagan Washington National Airport in Arlington County, Virginia. Mike Theiler / Retuers