"We've been offering either lower or less restricted fares for a year and a half," he added.

The highly restricted fares are valid for travel from April 1 through July 7.

But economists have done studies disputing this, and restricted fares are already at a historic low.

These fares, the airline says, are the same as restricted fares charged by other carriers.

The figure is higher in the busy summer season because vacation travelers like to take advantage of the restricted fares.

Since business travelers often have to change their schedules, a restricted fare poses a risk.

The accompanying graph gives some typical fares students pay at these agencies, compared with the lowest restricted fare available to the rest of the public.

However, until yesterday at least, some restricted fares on those routes were lower than the new ones.

Passengers paying restricted fares earn mileage that is good only for travel on Midway.

"Because you are on a restricted fare with certain conditions."