A Wal-Mart in Washington, D.C.. (AFP/Getty Images)

In the heated battle for e-commerce supremacy, Wal-Mart is not going to let Amazon’s latest gimmick go unanswered.

Last week, Amazon announced that it would hold Prime Day on July 15, a massive blitz of deals that it promises will feature more sales than Black Friday. The deals are to be available only to members of its Amazon Prime program, which charges $99 per year for free two-day shipping on millions of items.

Now Wal-Mart is hitting back, not only with some not-so-subtle criticism of Amazon’s offer, but with its own lineup of special offers.

In a Monday post on Wal-Mart’s company blog, a senior executive took shots at a sale format that requires paying a membership fee to unlock the deals.

“We’ve heard some retailers are charging $100 to get access to a sale. But the idea of asking customers to pay extra in order to save money just doesn’t add up for us,” writes Fernando Madeira, the chief executive of Wal-Mart.com.

Wal-Mart says it is rolling back its free-shipping minimum to $35 from $50 and says its customers will soon see some “special atomic deals,” though it did not explain what that meant.  Wal-Mart also emphasized that its shoppers will see thousands of new deals on “rollback” on Wednesday, the company’s term for price-slashing.

After Wal-Mart’s blog post, Amazon released a counterpunch.

“We’ve heard some retailers are charging higher prices for items in their physical stores than they do for the same items online,” said Greg Greeley, vice president of Amazon Prime in a statement. “The idea of charging your in-store customers more than your online customers doesn’t add up for us, but it’s a good reminder that you’re usually better off shopping online.”

Wal-Mart’s move underscores how intensely focused the company is on becoming a more serious competitor for online shoppers’ dollars. The company made $12.2 billion in online sales last year, significantly less than the $49 billion that the National Retail Federation estimates that Amazon made from retail sales in 2014. Wal-Mart has said previously that it is investing $1.2 billion this year into upping its e-commerce game.

Amazon’s sale is a one-day event commemorating its twentieth anniversary.  Wal-Mart rollbacks typically last for 90 days, and the company said the lower free shipping threshold will last “until further notice,” so it seems safe to say that the Wal-Mart promotion will run longer than Amazon’s.

[Wal-Mart is testing a free shipping program this summer]

Even as Wal-Mart declares that its deals come without an “admission fee,” the company is piloting a Prime-like program known as Wal-Mart Shipping Pass, which promises unlimited three-day shipping with the purchase of a $50 annual membership. For now, about 1 million best-selling items would be available under Shipping Pass, significantly less than the 20 million available for purchase with Amazon Prime.

Amazon’s chief executive, Jeffrey P. Bezos, owns The Washington Post.

Wal-Mart and Amazon aren’t the only retailers holding big July sales to get customers to open their wallets. Target’s “Black Friday in July” promotion is currently underway, while Best Buy has a similar promotion planned for July 24 and 25.

Correction: An earlier version of this post included an incorrect first name for Fernando Madeira.