Remember when Alphabet (NASDAQ:GOOG) (NASDAQ:GOOGL) subsidiary Google's then-CEO Eric Schmidt said that Amazon.com (NASDAQ:AMZN) was the search giant's biggest competitor? That sounded counterintuitive, since Google was aggressively competing with Apple at the time in the smartphone market, but Schmidt was referring to the fact that many of Google's most lucrative ads come from online shoppers looking for a specific product. If those users know that said product is available on Amazon, they'll simply head directly there, bypassing Google altogether.

More recently, Amazon has been ramping up its own advertising ambitions in a much more direct threat to Google. On the earnings call last month, CFO Brian Olsavsky noted that the growing advertising business was a "strong contributor to profitability." Adding insult to injury, it turns out that Amazon has stopped buying some ads on Google altogether.

Exterior shot of the Googleplex campus

Image source: Google.

Amazon is becoming a bigger player in advertising

Bloomberg reports that the e-commerce behemoth has stopped purchasing product listing ads, the type that appear at the top of Google search results when users are shopping for a specific item. These are among Google's most profitable offerings, and Amazon had started bidding on product listing ads back in 2016. Beyond losing direct ad revenue from Amazon, having such a prominent bidder pull out could even potentially hurt ad prices that Google earns from the remaining ad customers.

Amazon has an opportunity to win over advertiser spending from Google as it continues to grow its own advertising business. The company is smartly taking a measured approach, though, so as not to hurt the user experience with excessive ad load. Here's Olsavsky again from the call, responding to an analyst question about ad load (emphasis added):

On advertising. Let's step back a bit. It's now a multibillion-dollar program and growing very quickly. Our main goal here is to help customers discover new brands and products. When we show sponsored products, we're trying to show people things that they maybe wouldn't have seen otherwise in their normal search results. We're looking for a good balance here, as we said. We want customers to get the benefit of the new brand and product discovery. Then we want to let sellers, for both emerging and established brands, reach those customers. Those advertisers are all shapes and sizes with a main goal of, again, trying to reach our customers, whether to drive brand awareness, discovery, or hopefully purchase.

To be clear, the ongoing ad competition between Google and Amazon pales in comparison to other arenas where the companies butt heads. Voice commerce has emerged as a promising new way to make purchases, which has been a huge win for Amazon and Alexa. In March, Google announced a new program called Shopping Actions to challenge Amazon in voice commerce, allowing users to purchase products on the Google Assistant platform via voice.

Amazon and Google have a lot of battles waging concurrently, and advertising is just one of them.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Evan Niu, CFA owns shares of AAPL. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), Amazon, and AAPL. The Motley Fool has the following options: long January 2020 $150 calls on AAPL and short January 2020 $155 calls on AAPL. The Motley Fool has a disclosure policy.