Want to make sure you'll sit with your fiance or grab that aisle seat? Get ready to pay up.

Most airlines now offer so-called "preferred seating" where customers pay a fee for a few inches of extra legroom or to sit near the front of the plane. As more seats are blocked off as preferred, some customers may feel forced to pay the fees to make sure their family is seated together or to avoid the dreaded middle seats, Hobica said

Airlines say this is another example of "unbundling," where customers choose the "extras" that they are willing to pay for.

"The idea is allowing the customer to purchase what they're actually using," said Davien Anderson, a US Airways spokesman.

NEXT: United's FareLock fee