United Parcel Service Inc next year will join rival FedEx Corp in adding Sunday delivery services, efforts viewed as bids to fend off customer-turned-competitor Amazon.com Inc.

Atlanta-based package delivery firm UPS said on Tuesday it will start Sunday Ground deliveries on Jan. 1 for customers in the United States. UPS Express already delivers critical healthcare and other high-value shipments on Sunday.

UPS also will beef up its weekend services by dispatching more drivers on Saturdays, it said.

Customers are looking for seven-day delivery and faster service, spokesman Steve Gaut said.

Executives from UPS and FedEx repeatedly have said that they are not under threat from Amazon’s growing land, air and sea logistics network. Several experts and analysts who follow the companies disagree.

FedEx in June declined to renew its U.S. Express air shipping contract with Amazon. FedEx said Amazon accounted for less than 1.3% of FedEx’s revenue last year.

Cowen & Co analysts recently estimated that Amazon contributes about 10% of total revenue at UPS.