American Airlines's Cheap Fares Come With Restrictions Leave the carry-on at home and don't expect a window seat.

Move over Southwest, Spirit and JetBlue -- the U.S. has a new budget carrier: American Airlines.

The world's largest airline this week introduced new Basic Economy fares with the most basic passenger benefits.

Starting next month, customers in 10 select markets can pay the lowest available prices in exchange for a number of flying perks: seats are assigned at check-in (not chosen when booking), only one personal item (that fits under the seat) is allowed, you board the plane last and there are no upgrades, changes or refunds available.

Elite customers and eligible AAdvantage credit card members maintain a few added benefits like earning frequent flyer miles, though elite status qualifications are cut in half.

The on-board experience, meanwhile, remains the same -- you'll sit in regular Main Cabin seats, view the same in-flight entertainment and receive complimentary drinks and a snack.

"American Airlines now has something to offer every customer, from those who want simple, low-price travel to those who want an ultra-premium experience via First Class," company president Robert Isom said in a statement. "Importantly, this new fare product also gives American the ability to compete more effectively with the growing number of ultra low-cost carriers."

United and Delta also offer heavily discounted fares -- with most of the same restrictions as AA.

"Our goal is to make sure that all customers have the opportunity to purchase a ticket on American that works for their specific needs," Isom said. "We will work hard to ensure transparency, provide clear explanations of these fares, and we look forward to continuing to offer a wide variety of services to our customers."