UPS CEO Carol Tome said on a call with investors that Amazon is UPS’ largest customer, but it is not the company’s most profitable customer.

United Parcel Service forecast on Thursday downbeat 2025 revenue as it accelerates a plan to slash millions of deliveries for its largest customer, Amazon.com, a surprise move that sent shares tumbling as much as 18%.

United Parcel Service Inc. shares plunged after the company projected annual revenue well below expectations, telling investors that a long-awaited rebound in demand for its parcel services won’t arrive this year and prompting it to slash its low-margin business with Amazon.