American Airlines has announced it will terminate codeshare partnerships with Qatar Airways and Etihad Airways.
The move is seen as part of a dispute over state subsidies American claims these carriers receive from their governments.
Both the Middle Eastern carriers deny such claims.
American and other United States-based carrier, notably Delta Air Lines and United Airlines, argue government subsidies allow Qatar Airways, Etihad and Emirates to offer lower fares and more amenities to long-haul, international travellers.
American said cancelling code-sharing agreements with Qatar Airways and Etihad would not have a material financial impact.
The decision comes as Qatar Airways confirmed it would go ahead with plans to buy a stake in American Airlines.
The Middle Eastern carrier – which holds ten per cent of LATAM and a 20 per cent stake in British Airways-owner IAG - is seeking a ten per cent stake in its rival.
“Our stock purchase request and filing is going ahead as normal,” Qatar Airways chief executive Akbar al-Baker said.
Qatar Airways sent a revised antitrust filing to US regulators earlier seeking clearance to buy up to a ten per cent stake in American.
Qatar Airways, American Airlines, British Airways, Iberia and LATAM are all members of the one world airline alliance.