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Google has a new response to the antitrust scrutiny over its ad business. Following the new antitrust investigation announced by 50 U.S. attorneys general Monday, the company published a blog post Wednesday night arguing it competes in the ad tech sector with "lots of other companies" like Adobe, Amazon and Facebook. The new Google blog post, titled "The ad tech industry is crowded and competitive," was written in response to a Reuters piece Wednesday that discussed how advertising executives believed Google is stifling business. Among several other points, the Reuters piece said Google's running of search results, YouTube, Gmail and other services hinders advertising competition. It also touched on Google's bundling of ad tools that rivals claim make it so they can't afford to match. Critics of Google say the presence of other companies in the space isn't the issue. It's that Google has such a strong hold on different parts of the digital media supply chain. In fact, some of the companies Google used as examples of competition rebutted the company's argument in statements to CNBC. There's a lot left unsaid in Google's latest blog post about its dominance in digital advertising along with Facebook, and those are many of the areas the attorneys general will likely start looking into. Here's what's going on.

Google dominates online advertising

According to eMarketer, Google will reach a milestone of surpassing 20% of all U.S. ad spending both online and offline this year. Google captures 74.6% of U.S. search ad spending. And the company is expected to lead the U.S. digital ad market with a 37.2% share, totaling $48.05 billion this year. Regulators will likely examine whether Google has genuine competition among technologies along the links of the digital media supply chain, among other factors. Google's blog post, from its vice president of product management, Sissie Hsiao, only focuses on the presence of other digital advertising companies, not their market share and small valuations relative to Google's parent company Alphabet. "There are thousands of companies, large and small, working together and in competition with each other to power digital advertising across the web, each with different specialties and technologies," it says and names several companies involved in ad tech like AT&T, Comcast and Oracle. The post also cites publicly traded companies like Telaria, Rubicon Project and The Trade Desk. The market caps of Telaria ($451.4 million), Rubicon Project ($508.7 million) and The Trade Desk ($9.8 billion) are nothing to sniff at, but are tiny in comparison with Google's $854.1 billion market cap. But some argue that even if there is a proliferation of players that play in different areas of the ad tech ecosystem, Google is a huge player in each step of the way. The Trade Desk, for instance, said in response to Google's post that the tech giant's involvement in different parts of digital media make it "hard to be objective." "At The Trade Desk, we believe an open, competitive market for digital advertising increases effectiveness for advertisers, improves revenue for publishers and funds a broad scope of premium content for all consumers," the company said in an emailed statement. "As with many markets, it's hard to be objective if you operate on both the buy- and the sell-side of digital advertising, and that's key to an open, competitive market."

Google has power over how many ads are bought and sold online