LAST week, United Airlines announced a modification to its frequent-flyer programme, MileagePlus, that could change business travel as we know it. The shift is easy to understand: in the future, United will use the price of a ticket, rather than the distance flown, to calculate reward miles. That's not all: the more you spend, the more miles you'll get per dollar spent. This simple change has potentially huge consequences.

United isn't the first to make this change. Delta Air Lines announced something similar earlier this year. But it seems that competitors are following Delta's lead, rather than striking back. The end of mileage-based frequent flyer programmes may be in sight.

At issue is the fact that although most companies pay for business travel, employees generally get to keep the miles they earn. Longer flights are usually more expensive, of course, but few business travellers like to sit on a plane for any longer than necessary just to earn a few extra miles, so there isn't a big incentive to overpay. United's new policy changes that. Under this system, flyers will be tempted to pay as much as possible (after all, the company is footing the bill) in order to earn as many miles as they can. That's good for United. But in big companies, corporate travel managers—the folks charged with keeping travel expenses low—will be livid. United's new rules only make their jobs harder, and mean they have to keep a closer eye on trips booked with the carrier to make sure there's no funny business.

It is a big change. The backlash hasn't quite crystalised yet, but if other airlines follow, an already-unpopular industry will have to hope that sentiment doesn't harden towards it even further.