As Apple Inc. absorbs the regulatory body blow of a record $1.95 billion antitrust fine from the European Union on Monday, its legal team is bracing for yet another epochal action.

The U.S. Department of Justice is in the final stages of a years-long investigation into Apple AAPL, -2.43%, which could lead to a lawsuit as soon as this month.

The probe — which reportedly focuses on everything from the seamless integration between the iPhone and Apple Watch, to the company’s digital-payments system and its use of green text bubbles to differentiate Android text messages from iMessage communications — is nothing short of an all-out assault on Apple’s $2.8 trillion “walled garden” to its core.

Read more: Department of Justice edges toward antitrust case vs. Apple: report

The immediacy of the Justice Department lawsuit on the heels of the EU fine underscores an escalating crackdown on Big Tech by government agencies, after numerous attempts to legislate the tech industry have floundered. Justice officials aren’t just preparing a case against Apple — they are charging ahead on blockbuster lawsuit against Alphabet Inc.’s GOOGL, -2.49% GOOG, -2.56% Google digital-advertising business that will go to trial in early September. (The advertising case is the second major recent antitrust action targeting Google: A trial last fall challenged Google’s dominant role as the default search engine on millions of devices.)

Read more: Justice Department sues Google for antitrust in digital advertising, while Alphabet stock slides

Also: Google spent billions to build an illegal monopoly, Justice Department says as trial gets under way

At the same time, the Federal Trade Commission and 17 state attorneys general in September sued Amazon.com Inc. AMZN, -0.05%, alleging the company is a “monopolist that uses a set of interlocking anticompetitive and unfair strategies to illegally maintain its monopoly power.”

Read more: Amazon sued by FTC, which alleges the company is ‘exploiting its monopoly power’

To complicate matters even further, tech companies must comply with the EU’s Digital Markets Act, which makes large players in ad tech accountable for user data they collect and use in the European Union. The DMA goes into effect March 6.