"Delta says that there's $400 million of incremental revenue available from an immunized JAL-Delta joint venture. Where does this $400 million come from? It's going to come from the pockets of business travelers," Mitchell said.

The deal would lessen the viability American's oneworld alliance as a competitor in Asia, leaving Delta with SkyTeam and United Airlines with its Star Alliance, Mitchell said.

United Airlines with partners Continental and All Nippon Airways have already applied for antitrust immunity, and American would apply if it is selected to continue as JAL's partner. A JAL deal with Delta is seen as the harder sell because it would create a larger market concentration.

American has encountered its own challenges to a bid for antitrust immunity in a partnership with British Airways and Spanish carrier Iberia. Delta already has antitrust approval of a similar joint venture with Air France/KLM.

In a separate antitrust immunity case, Delta is seeking approval for a partnership with Australian carrier Virgin Blue. The Department of Transportation late last year asked for more information before it makes a decision.

Delta's newfound market power has also been an issue domestically. The carrier has encountered opposition to a proposed deal with US Airways that would expand Delta's presence in New York significantly.

Delta and US Airways last August said they had reached agreement for Delta to give 42 slot pairs at Washington's Reagan National Airport to US Airways in exchange for 125 slot pairs at New York's La Guardia Airport, to cement what Delta would call a "domestic hub" at La Guardia and a larger presence for US Airways in Washington, instead of competing against each other tooth-and-nail at both.