The term “business class,” especially to infrequent fliers, may evoke the image of luxury on planes with good free food and drink, along with an actual comfortable seat.

In actuality, while business class is almost — but not always — better than coach, the product varies widely, especially for domestic flights.

On some planes, while the onboard service is a plus, many travelers would say that a good exit row seat in back is preferable. (On many flights, exit rows in coach have significantly more legroom than in first or business.) On occasional flights there’s the chance for an empty row with space that beats business class.

On the other hand, some business-class seats in the U.S. are particularly nice. Nowhere is the competition more fierce than on the transcontinental routes, specifically JFK to Los Angeles and San Francisco.

United Airlines is following American and Delta by announcing that they will have lie-flat business-class seats, which they dub “P.S.” (Premium Service) for these transcontinental flights. The seats will have WiFi, in-seat power, USB ports and on-demand entertainment. What’s not to like?

On these planes with lie-flat seats, there will now be 28 business-class seats, with no first class, 48 Economy Plus seats and 66 seats in regular coach. This compares to the current P.S. planes with 26 business class seats and 12 in first, along with 66 seats in an ALL Economy-Plus cabin.

The translation: There are going to be a lot fewer good seats. Since United introduced the P.S. service, it has been a treat for fliers, frequent and infrequent, since even the coach seats have been better than average with more legroom.

United doesn’t allow automatic free standby upgrades on the P.S. service, which means the only chance to get up front with a coach ticket is using miles or “Regional” upgrades. These are given in small quantities to the most elite fliers. So, fewer people have been chasing those upgrades.

With other United, non-P.S., service, even travelers who haven’t held the highest elite status have often been able to get in business class, which almost never happens on other popular routes where elites get automatic standby upgrades. As an added occasional benefit, United has perhaps been slightly overbooking business class, as I’ve had several clients who’ve booked paid business class and been upgraded to first, for free.

(As an aside, airlines for years have sometimes overbooked the back sections of planes when there are a lot of empty seats up front, figuring they would rather have the extra revenue and, worst case, give away some free food and drink.)

However, with the new planes configured with 28 front-cabin seats as opposed to 38, passengers trying to upgrade are going to have a much harder time. (Something similar happened when United modified some of their 777s to include business-class flat-bed seats, but took the seat count from 49 to 40. And a lot of fliers suddenly found themselves stuck in coach.) Plus, those who book late, even elite fliers, are more likely to end up in a cramped seat with regular legroom.

Infrequent fliers may not notice the changes, but in my experience, many business travelers choose the P.S. service over other carriers (and United’s Newark service) just because they KNOW, worst case, they will have an Economy Plus seat.

Clearly, United is betting that both improving and reducing the number of premium seats will increase the number of people who will actually pay for those seats.

Nonetheless, expect the whining to begin.