The promotion will begin in June and run through January; to qualify, sellers will need to have sold 60 or more of a product per month or have products specifically selected by Amazon. They’ll also have to keep the level of inventory they supply to Amazon at a certain level.

Here’s what it means: The push for one-day free shipping can’t be a unilateral move by Amazon: It’ll need sellers to work with it.
One-day shipping is likely feasible for Amazon, but more than half its sales come from third-party sellers, making them critical to achieving this new goal. Third-party merchants were responsible for 58% of Amazon’s sales in 2018, an enormous jump from 3% in 1999.
Because of this, if Amazon wants to have any chance of making the lion’s share of the items on its marketplace available for one-day delivery, it’ll need help from those sellers. It shouldn’t be too difficult to get them on board, though, given that one-day shipping is likely to increase consumers’ enthusiasm for Amazon, leading to more sales for the sellers working with it.
The bigger picture: Amazon’s one-day shipping goal will highlight the importance of its relationship with sellers (both FBA and FBM doing their own ecommerce order fulfillment) as well as the fine-grain control it has over its private-label products.