It's unclear what specific charges the EU will bring against Google, but it's believed the charges will focus on whether Google used its dominance in the search market to favor its own results. In the memo, Google lays out its case, essentially arguing that its services (Google Shopping, specifically) are already open to competition. From the memo:

The competition is just one click away — and it’s growing. People can use Bing, Yahoo, Quora, DuckDuckGo, and a new wave of search assistants like Apple’s Siri and Microsoft’s Cortana, as well as more specialized services like Amazon, Idealo, Le Guide, Expedia, or eBay. In addition, users increasingly turn to social networks like Facebook and Twitter to find news and suggestions — where to eat or which movies to watch.The memo does not bring up any allegations about the company favoring its own results. (Key members of the FTC brought up such complaints against Google, although the agency ultimately decided against suing.)The memo continues:

Mobile is changing everything — with the explosion of apps taking people directly to the information they want. Today 7 out of every 8 minutes on mobile devices is spent within apps. Yelp, for example, has said that over 40% of its traffic comes direct from its mobile app.Competition online is thriving — despite what many of the complainants in this case allege. Indeed if you look at shopping, it’s clear that there’s a ton of competition (including from Amazon and eBay) that has not been harmed by Google’s own shopping service.Google goes on to reproduce charts showing the rise of rivals like Amazon, but does not include some of the facts that have most concerned regulators. Google holds about a 90 percent market share of search in Europe, and antitrust charges have been years in the making. The Commission is expected to also open a formal investigation into Android, which Google, in the memo, says "is just the start of a process and does not mean the EC will necessarily take action." The document also asks that employees not comment "on pending legal issues, internally or externally."

Whatever the specific charges, Google is facing a fight: the company could be looking at more than $6 billion in penalties.