As competition increases in the rapidly expanding food delivery business, Amazon is playing for keeps.

Before, Amazon charged Prime members a $14.99 monthly subscription fee for its Amazon Fresh online grocery delivery service while two-hour Whole Foods deliveries were free for Prime customers through Amazon’s Prime Now delivery app. But starting Tuesday, grocery delivery from Amazon Fresh is free, albeit in phases.

Prime members who have not ordered groceries using the service can request an invitation. The delivery minimum for the Amazon Fresh service is $50 in New York City and $35 in a most other regions where the service is available.

Additionally, customers will be able to buy Whole Foods groceries through Amazon.com and the Amazon app, in addition to the Prime Now app. New customers will have to get an invitation if they want groceries delivered from the chain through Amazon’s website and app, though.

This places Amazon in fierce competition with competitors including Instacart, Walmart, Kroger and FreshDirect. Additionally, Amazon’s price reduction pressures its largest rival, Walmart, which charges a $98 annual fee for grocery delivery.

Walmart also has a feature that allows employees to place groceries inside customer’s refrigerators while they’re away from home.