New York (CNN Business) Amazon is eliminating its fee for grocery delivery in the United States as competition heats up in the rapidly expanding food delivery business.

Before today, Amazon charged Prime members a $14.99 monthly subscription fee for its Amazon Fresh online grocery delivery service. Two-hour Whole Foods deliveries were free for many Prime customers through Amazon's Prime Now delivery app.

Starting Tuesday, grocery delivery from Amazon Fresh is free for Prime members who have previously used the grocery-delivery service.

Amazon is rolling out the new, free service in phases: Prime members who haven't yet ordered groceries can request an invitation. Amazon didn't say when it will start taking on new grocery-delivery customers.

The delivery minimum for the Amazon Fresh service is $50 in New York City and $35 in a majority of the other 2,000 regions the service is available in.