(Image Credit: Joe Raedle/Getty Images)

United Airlines quietly raised the fee for a second checked bag earlier this month from $70 to $100 on some international flights.

Passengers traveling on trans-Atlantic routes between North, Central and South America and Europe, the Middle East, India and selected countries in Africa will see the increase. On those routes, the first checked bag is free of charge.

Passengers traveling from the United States (except Hawaii) will pay $100 for the second checked bag to Europe, the Middle East, Africa and India but $70 to South America (except Brazil and Venezuela) and $40 to Central America.

Confused yet? Here's a link to a chart outlining the new fees on United's website.

United raised the fees on these routes from $50 to $70 a year ago. This latest increase matches the one Delta made earlier this year when it raised second checked bag fees on the same routes.

The new fee applies only to tickets purchased after June 1, 2012.

Summer airfare to Europe is up 11 percent, according to Kayak.com.