United Airlines and US Airways are following the lead of American Airlines, which makes customers pay $15 for the first checked bag. United's new fee begins Friday, June 20, for customers buying domestic tickets for August 18th or later. It does not apply to first or business class, or those with premiere status. Us Airways' new baggage fee kicks in for tickets booked on or after July 9th. Most airlines are already charging $25 for a second checked bag.