United Airline fliers will soon get the chance to buy cheaper fares on some of the airline's flights. But as good as that sounds, those tickets will come with strict rules that might not make it appealing for some passengers.

The airline's new fare option, disclosed Tuesday, is called Basic Economy and limits what bags you can bring on board and doesn't allow you to choose your seat. United said Basic Economy fares will cost less than its regular economy class, but declined to say by how much. The new fares are expected to go on sale early next year for flights taking place in the spring. At first, Basic Economy will only be available for U.S. flights between certain cities. The airline will continue to offer its regular economy fares, as well as Economy Plus with more leg room and its first class options.

Here's what you need to know about Basic Economy fares:

NO SEAT CHOICE

Your seat will be automatically chosen for you when you check in. That means you'll likely be stuck with the seat that other economy passengers didn't want -- so be prepared to squeeze into a middle seat. And if you plan to fly with friends or family, and want to sit next to them, Basic Economy is not for you. The airline said it's unlikely you'll be able to sit together. Also keep in mind, Basic Economy passengers will be the last to board the plane.

NO CARRY-ON BAGS

Carry-on bags that need to be stuffed into the overhead compartments won't be allowed on the plane. Basic Economy fliers can only bring a bag on board that fits under the seat, like a purse, laptop bag or backpack. If you bring anything bigger, you will be charged a fee and the bag will be checked in. That's much different from regular economy fliers who can still bring a carry-on aboard for free, as well as a small bag.

NO TICKET CHANGES

Once you buy a Basic Economy ticket, it can't be changed or refunded. If you do need to switch flights, you'll lose the money you paid and have to buy another flight. That's much different from United's other fare classes, which allow fliers to make changes for a fee.

SAME INFLIGHT SERVICE

Basic Economy fliers will get free snacks or drinks if they're offered on the flight, just like other economy passengers. They'll also be able to buy meals or WiFi access, if it's available.