The fight for e-commerce supremacy doesn't take days off and does not wait for the holiday season.

Amazon has announced a sale for July 15, it says, will be "filled with more deals than Black Friday," but it's for one day only and only available to Amazon Prime members.

In response, Walmart has announced a very similar sale, also on July 15, for its online products.

Walmart is billing its sale as more inclusive, writing in its promotions, "You shouldn't have to pay $100 to get great deals," referring to Amazon's annual $99 fee to be a Prime member.

Walmart's yet unnamed Day of Rollbacks is also slated to last longer than Amazon's Prime Day.

"This metal frame pool on rollback, you save $80!" said someone in a Walmart promotional video.

Walmart has rollback sales throughout the year, and they usually last about three months. And while rollback prices are lower, they're not usually as low as Walmart's Black Friday deals. But neither company has specified prices nor announced which items will be on sale.

Along with the rollback prices, Walmart is dropping its free shipping minimum order to $35 from $50. Coincidentally, $35 just so happens to be the minimum order price to get Amazon's free shipping.

Walmart.com CEO and President Fernando Madeira wrote on Walmart's blog, "We're standing up for our customers and everyone else who sees no rhyme or reason for paying a premium to save."

Now despite the CEO's corporate fighting words, signing up for Amazon's Prime service comes with more than just entry to this one-day sale. It gives users access to movies, TV shows, free shipping and other perks.

But Walmart is fighting an uphill battle with Amazon for e-commerce business. In 2014, Walmart increased its e-commerce sales 22 percent, bringing its online revenue to $12 billion. During that same year, Amazon brought in almost $89 billion in net sales.

This video contains images from Mike Mozart / CC BY 2.0  and Getty Images.