FedEx said it will start delivering packages through its new Sunday ground service this weekend as it competes with Amazon and other courier services.

The company had announced the move in May. FedEx has long provided residential Sunday delivery during the peak holiday season, but now the service will be available year-round for "the majority of the US population," the company said previously.

The move comes as e-commerce has upended the delivery market, flooding the United States with packages. Amazon's in-house delivery network delivers about half of its own packages, according to an analysis published by Morgan Stanley in December. And UPS began its own Sunday delivery service as of Jan. 1.

The report estimated that Amazon will deliver 6.5 billion packages per year by 2022, surpassing UPS at 5 billion packages and FedEx at 3.4 billion packages.

FedEx and Amazon have recently knocked heads. Last month, just as the holiday season was heating up, Amazon briefly banned third-party sellers from using FedEx Ground, citing its poor delivery performance. Last week, Amazon reinstated FedEx Ground and FedEx Home as shipping options for its customers.

FedEx's decision to expand its service could be a gamble given that Amazon has its own delivery brand. And Amazon's cargo airline, Amazon Air, is expected to complete a $1.5 billion air hub in northern Kentucky. by 2021. According to Jeff Bezos, the hub could employ 2,000 workers.