(Reuters) -Three U.S. airlines on Wednesday warned of higher fuel costs in the third quarter due to a jump in crude prices, adding to the pressures the industry already faces from expensive labor contracts.

While Alaska Air Group cut its pre-tax margin forecast for the quarter, Southwest Airlines said it continues to expect a "solid profit".

United Airlines said it expects capacity, operating revenue and cost per available seat mile, excluding fuel, in the third quarter to be consistent with its earlier guidance.

Alaska Air expects a third-quarter adjusted pre-tax margin of 10% to 12%, lower than its prior expectation of 14% to 16%.

The Washington State-based carrier also revised its estimate for revenue growth in the third quarter to 1% to 2%, from flat to 3%.

Shares of Southwest Airlines fell 4.3% before the bell.

(Reporting by Mehr Bedi in Bengaluru; Editing by Pooja Desai)