Amazon on Sunday announced that it would begin to put new grocery delivery customers on a wait list and limit the shopping hours at some Whole Foods stores to prioritize orders from existing online customers.

"We are temporarily asking new Amazon Fresh and Whole Foods Market delivery and pickup customers to sign up for an invitation to use online grocery delivery and pickup. We’re increasing capacity each week and will invite new customers to shop every week," Amazon said.

In the coming weeks, Amazon will launch a new feature that will allow customers to secure time to shop. This feature will give delivery customers a virtual “place in line” and will allow the company to distribute the delivery windows on a first come, first served basis.

Shoppers have recently reported that they could not place orders due to a lack of available delivery slots. Amazon said it would have to relegate all new online grocery customers to a wait list starting Monday while working on adding capacity each week.

In recent weeks, Amazon increased the number of Whole Foods stores offering grocery pickup ​to more than 150 locations, up from 80 previously.

"We are releasing delivery windows throughout the day and have made it easier for customers to see when the next delivery window is available by including it on the homepages of Amazon Fresh and Whole Foods Market," Amazon added.

Amazon offers grocery delivery services Amazon Fresh and Amazon Prime Now from its own warehouses and Whole Foods stores. It typically touts ultra-fast delivery within hours, ​with shoppers able to choose a delivery window. Last month, Amazon temporarily suspended the Prime Pantry delivery service, which sells non-perishable groceries.