How low can free shipping go?

The latest war of one-upmanship between Amazon and everyone else is over free shipping fees — with the e-commerce giant recently lowering to $25 the minimum purchase required for non-Prime customers to get free shipping.

It had been $35.

The one rub is that some purchases under the new plan may take five to eight days to arrive.

It’s the second time in less than three months that Amazon — led by CEO Jeff Bezos — has reduced its free shipping minimum, according to BestBlackFriday.com, a shopping blog that first reported the new policy.

In February, Amazon lowered its free shipping minimum to $35, down from $49 — likely in response to Walmart, which had lowered its minimum to $35 for free two-day delivery.

“Amazon understands their data better than any retailer in the industry,” said Sarah Engel, chief marketing officer of DynamicAction, a retail analytics firm. “With this move they are trying to get back their non-Prime shoppers who they may be losing [to] other retailers like Walmart.”

Prior, Walmart charged a $49 annual fee for free shipping.