NEW YORK - United Airlines unveiled on Thursday a second-bag fee for passengers on some international routes, following a trend set by U.S. Airways Group Inc and Continental Airlines.

Passengers flying trans-Atlantic routes will pay $50 for a second bag at the airport or $45 if purchased on the carrier's website. This applies on routes going from the United States, Mexico and the Caribbean to Europe and back.

Travelers going from the United States to Mexico or the Caribbean will pay slightly less -- $30 at the airport and $27 online.

With the implementation of this new policy, United is matching other U.S. airlines who have previously announced a fee for checking a second bag for trans-Atlantic travel, the carrier said in a note to employees on Thursday.

In late August, U.S. Airways added a $50 fee for a second checked bag, while Continental added a $50 fee for some economy ticket holders.

Bag fees have been one source of cash for U.S. airlines as they attempt to counter the decline in passenger traffic in recent months. United Airlines' parent UAL Corp reported a nearly 6 percent drop in traffic last month. (Reporting by Deepa Seetharaman; Editing by Gary Hill)