As last week's launch of a 45% Amazon Prime subscription fee discount for those relying on food stamps and other government-assistance programs shows, Amazon.com Inc. (AMZN) is eager to pull out all the stops to slow down Walmart's (WMT) suddenly resurgent e-commerce operations, and more broadly grow Prime's reach among lower-income consumers. The launch of a Prime service catering to debit card users adds to this effort.

Prime Reload, announced on June 12, adds an automatic 2% to funds contributed by Prime members to a digital "gift card balance" using a checking account or debit card. Setting up the service is simply a matter of providing bank account, debit card and driver's license information.

The 2% bonus is less than the 5% discount Amazon provides for purchases made on its site using the Prime Rewards credit card (backed by Visa Inc. (V) ) or the Prime Store Card. But for those who prefer not to sign up for one of those credit cards, or who are unable to due to poor credit, Prime Reload could be a compelling option.

And from Amazon's perspective, a 2% bonus could still be less than the additional processing fees it would have to pay if a transaction was made with a non-Amazon credit card. In addition, the company can -- much like a bank -- collect interest on gift card balance funds that haven't been spent, and use them as a source of working capital.

In addition to making new attempts to get lower-income customers to adopt Prime, Amazon has stepped up its attempts to grow sales to customers lacking Prime. These include the April launch of Amazon Cash, a service that lets those lacking a bank card add between $15 and $500 to their Amazon balance at retailers such as CVS Health Corp. (CVS) , GameStop Corp. (GME) and Family Fare Supermarkets (more retailers will be added in time). As well as gradually slashing the free shipping minimum for non-Prime shoppers to $25 from $49, after hiking it from $35 to $49 in early 2016.

All of these moves come as Walmart's e-commerce sales accelerate sharply under the oversight of former Jet.com CEO Marc Lore. With the help of a big expansion of Walmart's online merchandise lineup, the introduction of free 2-day shipping for $35-plus orders involving over 2 million items and discounts for in-store pickups, Walmart's e-commerce revenue rose 63% annually in the April quarter, a big improvement from the prior quarter's 29%.

Still, consumer products research firm Euromonitor estimates Walmart had just 7.6% of the U.S. e-commerce market in 2016 to Amazon's 33%. And thanks in large part to Prime's momentum and tremendous seller marketplace growth, Amazon's North American segment revenue rose 24% annually in Q1 to $21 billion. That's soundly above the roughly 15% growth comScore estimates for the total U.S. e-commerce market.

Though Walmart seems to be influencing Amazon's moves, Jeff Bezos' company is likely also driven by a realization that better penetrating lower-income consumers is crucial to keeping its U.S. growth near current levels, given how Amazon has already become a way of life for a larger percentage of more affluent consumers. A recent Piper Jaffray survey indicated 82% of U.S. households earning $112,000 per year or more are now signed up for Prime, more than twice as many as were signed up as of 2013. And that the percentage of households earning $67,000 to $112,000 that are signed up for Prime has roughly doubled over this time to 67%

By contrast, Prime's penetration drops to 54% for those households with incomes of $41,000 to $68,000, and 52% for those with incomes of $21,000 to $41,000. Altogether, Piper's survey indicates about 60% of U.S. households are now signed up for Prime. That estimate might be a little high, given there are about 125 million households in the country. A fall 2016 Cowen survey indicated there were 50 million U.S. Prime members, and Morgan Stanley (relying on Amazon's 2016 annual report disclosures) estimated in February that there are 65 million Prime subs globally.

Either way, between Prime's demographics and how much more Prime members spend on Amazon relative to non-members, all signs point to Amazon's sales skewing heavily towards higher-income online shoppers. The company has good incentives to reduce that skew -- especially if it can slow Walmart's momentum along the way.