The U.S. Department of Justice shed more light on a proposed joint venture between United Airlines, a unit of UAL Corp. (UAUA), and Continental Airlines, Inc. (CAL), when it commented on their plan.

"Continental and United hope eventually to codeshare on nearly all of their domestic flight segments, combine customer lounges, consolidate their operations at common airports, provide frequent flyer reciprocity, cooperate on ticketing, reservations and check-in and perform joint procurement," the DOJ wrote Friday. With codesharing, the airlines can sell tickets for each other's flights.

The nation's third-largest and fourth-largest airlines held merger talks but last year decided to form a close, but less costly, union. The airlines haven't provided details on the business deal they said would allow them to add revenue and cut costs.

While some U.S. airlines have formed partnerships with other carriers, the deal between United and Continental would be unique among major U.S. carriers.

The Justice Department didn't comment on that plan in a document that mainly focused on the carriers' request to the U.S. Department of Transportation for anti-trust immunity on international routes. The DOJ said the anti-trust immunity request should be denied.

It said an international partnership not subject to antitrust laws would limit international competition and could have implications for the U.S. market.

The airlines said Monday that they still expect to get antitrust immunity.

Continental has already arranged to switch in October to the Star global airline alliance - where United is a major player - from the SkyTeam alliance.

The airlines' domestic pact wouldn't depend on whether they get antitrust immunity. Continental and United haven't given a timetable for rolling out a domestic partnership.

When Delta Air Lines Inc. (DAL) last year merged with Northwest Airlines to become the world's largest carrier, United and Continental also held merger talks but called them off as the economy turned sour.

Most airlines have joined alliances to further international business, since cross-border mergers are barred by national laws.

Following a period for public comment on the DOJ's conclusions, the Department of Transportation will continue its deliberations.

-By Ann Keeton; Dow Jones Newswires; 312-750-4120;ann.keeton@dowjones.com