Snagging a great airfare doesn't mean you'll have a great seat on your flight.

Starting this Friday, coach passengers on United Airlines who want to avoid the back of the plane may have to pay up for it. The airline will charge a fee for so-called preferred seats on flights throughout its network. These seats don't come with extra legroom or other perks. They're standard economy seats that will be behind the Economy Plus rows, which come with more space.

United's rivals American Airlines and Delta Air Lines already have a surcharge in place for such seats. The trend is part of airline's efforts to segment their coach-class cabins, an effort to get travelers to pay up for perks that used to be included in airfare. Airlines already offer travelers add-ons such as early boarding, lounge access and more legroom.

United did not say how much more travelers would have to pay for seats in these preferred locations. On competitors Delta and American, the prices vary by aircraft, route and demand. For example, a preferred seat on a Delta flight from New York to Los Angeles in early January was $80. On an American flight from New York to Paris at that time, the price of a preferred location seat ranged from $62 to $81. Prices are for each leg of the itinerary.