Walmart can’t call an Uber anymore.

Uber Technologies Inc. is ending a two-year-old pact to have its drivers handle grocery deliveries for Walmart Inc. across four U.S. cities, Walmart (WMT.N) spokeswoman Molly Blakeman said Tuesday. Uber’s final day will be June 30 and deliveries in those markets will be handled instead by Walmart’s other providers including Deliv, DoorDash Inc. and Postmates Inc.

“Customers shouldn’t notice any difference as the transition takes place,” Blakeman said in an email, declining to provide a reason for Uber’s decision.

The defection is a hiccup for Walmart’s online grocery service, which is expanding this year from six cities to more than 100 markets to battle Amazon.com Inc. (AMZN.O), Instacart Inc.’s network of grocers and Target (TGT.N). The program has been a hit with shoppers, and Walmart sees it as a way to get more of its regular customers buying online, where they spend twice as much as in the store. Walmart’s web business stumbled from logistical snafus during the holiday period, so investors are looking at next week’s first-quarter results to show some improvement.

Uber handled deliveries in Dallas, Phoenix, Tampa and Orlando, with customers paying a US$9.95 fee with a US$30 minimum order. Walmart executives always called the Uber arrangement a test, along with other experiments, like asking store employees to deliver orders on their way home after work. Walmart also had a short-lived pilot with Uber rival Lyft Inc., which ended in 2016.

The termination of the Uber deal was reported earlier by Reuters. A spokesman for Uber didn’t immediately reply to a request for comment.