CHICAGO — Baggage fees are fast becoming an unavoidable part of U.S. flying: Three of the largest carriers now charge $15 for a first checked bag.

No. 2 United Airlines and No. 7 US Airways announced their new fees on Thursday, three weeks after No. 1 American Airlines set the precedent for the charge.

Most U.S. carriers already have instituted a $25 charge for checking a second bag — part of a potpourri of new fees that reflect a struggling airline industry passing along record fuel prices to passengers in the form of higher fares, fuel surcharges and service charges.

As of July 1, Southwest Airlines will be the only U.S. carrier that permits two checked bags for free, according to air travel expert Tom Parsons, who expects still more service fees to come.

"The major airlines are truly a la carte now — you don't get anything free any more," said Parsons, chief executive of the travel Web site Bestfares.com.

UAL Corp.'s United said its baggage fee goes into place with customers who buy tickets beginning Friday for domestic flights of Aug. 18 or later. It does not apply to customers flying in first or business class or those who have premier status with United or Star Alliance, and first and second bags will still be free for itineraries that include international flights, aside from Canada.

US Airways' new fee takes place for tickets booked on or after July 9. The carrier also said it would cut domestic flights, shrink the size of its fleet, slash 1,700 jobs and add a fee for nonalcoholic drinks during flights.

"We must write a new playbook for running a profitable airline in this new and challenging environment," US Airways Chairman and Chief Executive Doug Parker said in a statement.