Airlines Increase Re-booking Fee
This went into effect in April for United, with that fee applying for US and Canadian flights while increasing the change fee from $250 to $300 for some international travel, according to USA Today. United appears to have started the trend which has now reached the four airlines.
Our NY Senator Chuck Schumer caught wind of this and is apparently not too happy. Not sure if he'll be able to help regulate the private airlines (doubtful) but he's calling on them to reduce the fees again.
This site gives an interesting history of why the fees have steadily increased (stemming, possibly, from business travel).
Also, mayhaps slightly out of date, but this is a nice wrap up by USA Today of airline fees, ranging from checking bags to changing flights.