Amazon will stop making Prime Now deliveries via bicycle courier in its hometown of Seattle after this Saturday, shifting entirely to vehicle delivery instead, according to messages sent Wednesday to bicycle couriers from their contracting firms, informing them of Amazon’s decision.

The move will affect about 40 bicycle couriers who carried packages for Amazon’s one- and two-hour delivery program in the city. One contracting firm told couriers in an email that the bike delivery program in Seattle was an exception, and that Amazon’s shift to full vehicle delivery was intended to create a more uniform process for its Prime Now cities.

(Editor’s Note: The number of affected couriers has been corrected since the original post.)

The abrupt decision, with only three days’ notice, caught bicycle couriers off guard. One firm said it was possible but unlikely that Amazon could reverse its decision at some point in the future.

As reported by GeekWire last fall, expectations for the Amazon bike couriers were high — with heavier-than-normal loads, fast delivery times, careful tracking by the system, and a requirement for near-perfect execution. Riders are assigned a numeric score that Amazon calls the “Perfect Delivery Rate,” or PDR, describing how well they meet expectations.

Amazon has been aggressively developing its own delivery and transportation infrastructure, and the company often tests new initiatives in Seattle, where it’s headquartered.

The company previously discontinued bike deliveries for its Amazon Fresh grocery service. We’ve contacted Amazon for comment on the decision, and we’ll update this post when we hear back from the company.