United Mileage Plus, Lufthansa Miles & More, and Northwest WorldPerks are each offering members a chance to earn free economy-class tickets to anywhere they fly … but there is a catch.

To get the tickets, members must register for the promotion, then fly on a paid, published first- or business-class roundtrip ticket from the United States to Europe by April 15. With United and Lufthansa, qualifying flights include any flight booked in F, A, C or D classes, and on Northwest the qualifying flight must be booked in J class. For every qualifying roundtrip a member takes, they will earn one free, non-upgradeable economy-class ticket to anywhere the respective airline flies.

That’s right, non-upgradeable — as in, if you want to use your free ticket to fly from Toledo to Tokyo, you’re going to be spending upwards of 15 hours cramped in coach.

On the other hand, the free tickets are transferable and both programs allow members to earn multiple tickets (United and Lufthansa have placed no restrictions on the number of free tickets that can be earned by a member, and Northwest only limits earning to one free ticket a day during the promotional period).

While this promotion probably won’t cause anyone to run out and start buying bunches of first- and business-class tickets to Europe, it might influence some business travelers to choose United, Lufthansa or Northwest over competing airlines — especially those business travelers who enjoy giving away tickets as gifts, or who don’t mind bruising their knees when traveling for leisure.