Delta Air Lines and Alaska Airlines customers will be losing one way of earning frequent flyer miles starting next spring, as the two airlines are ending their codesharing and frequent flyer partnerships. 

The two carriers announced Monday that starting May 1, they will no longer codeshare on flights and will end customers’ ability to earn frequent flyer miles when traveling with the other carrier.

Under a codeshare agreement, airlines will typically share the same flight, which is published and sold under each airline’s individual designation and flight number. For example, a customer could by a ticket on Delta for a flight operated by Alaska along a route that Delta does not typically operate.

In recent years the agreement between the companies has come into question, USA Today reports, as Delta began building a hub of its own in Seattle, where Alaska was located. As a result, the two airlines began operating competing flights on the same routes.

“This should come as no surprise as our relationship has become increasingly competitive over the last few years,” Charles Breer, managing director of alliances for Alaska said in a statement. “Given our own growth and expansion, Alaska Airlines now can take people virtually anywhere they need to go.”

While the termination of the codeshare agreement might not affect customers in terms of available flights, it will end one customer-centric feature: frequent flyer mile accumulation. Through Alaska and Delta’s agreement, customers’ frequent flyer miles are essentially merged, allowing them to rack up points from one carrier or the other. That will cease April 30, 2017.

For Delta customers the termination of the partnership means that travelers will no longer be able to earn and redeem Delta miles or Mileage Plan miles on flights operated by the other carrier.

Delta SkyMiles Members will be able to earn and redeem miles on flights operated by Alaska through April 30, 2017. SkyMiles Medallion Members will continue to receive their benefits when flying with Alaska through April 30, 2017.

Starting May 1, SkyMiles Members will not be able to earn and redeem miles on flights operated by Alaska unless a ticket was purchased before Dec. 19, 2016.

Alaska also outlined how the changes would affect its frequent flying customers. Like Delta customers, passengers who have already booked flights on Delta will still earn Alaska points for those flights. Those who are about to book travel must complete their trip before April 30, 2017 to earn miles.

Customers can redeem miles for award travel on Delta as long as those trips are booked and completed before April 30, 2017.

In addition to making changes to its frequent flyer program as far as Delta is concerned, Alaska reminded customer of other upcoming revamps.

For example, starting today, travelers with the airline can now earn Alaska Air mileage for flights operated by Virgin America, and vice versa.

Additionally, the carrier says that it has reduced the number of miles customers must redeem for short, one-way flights to as low as 5,000 miles. The airline also increased the number of miles its flyers earn on flights operated by other codeshare partners British Airways, Cathay Pacific, Emirates, and others.

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