The next time you book a flight with points, double-check fare you're booking: t might be basic economy.

A growing number of U.S. airlines now offer basic award fares. That means — even if you're using miles — you could face restrictions like no seat selection, no lounge access and no upgrades.

For years, Delta Air Lines was the only carrier in America with "basic" mileage redemptions.

Then last year, both JetBlue and Southwest Airlines started offering up no-frills award tickets.

What this means for travelers: increasingly, when you go to search for a mileage deal, the cheapest award price you'll see is often a restrictive basic ticket.

And with nearly every major airline shaking up their basic economy policies in recent months, I wouldn't be surprised if more airlines follow suit.

This affects the number of points in your account, the loyalty perks you'll get when you fly, and your ability to make changes to your itinerary after booking.

Three of the six largest U.S. airlines now offer a basic economy product even to customers booking with points and miles: