The Seattle company has offered free shipping on qualifying orders over $35, but with a catch -- all products in a basket had to come from the same seller.
But the retailer said Tuesday that items from multiple merchants -- including those that don't ship through Amazon -- could be combined to qualify for the free shipping minimum. That triples the number of items that can contribute to free shipping, Amazon said.
Qualifying items are labeled with "Free Shipping" on its product page.
E-commerce players such as Amazon and Google and bricks-and-mortar retailers have been scrambling to offer shoppers faster and cheaper shipping.
Amazon has been opening distribution centers around the country to speed up shipping and expand same-day deliveries. The company said this month that its customers saved $2 billion in shipping fees during the holiday season.