Alphabet Inc. Class C (GOOGL.US) has been accused by the U.S. government of abusing its dominant position in the advertising market, further engulfing it in an antitrust storm.

A federal judge in the United States ruled on Thursday that Alphabet Inc. Class C, a subsidiary of Alphabet (GOOG.US, GOOGL.US), abused its dominant position in two online advertising markets, violating U.S. antitrust laws. This is another setback for Alphabet Inc. Class C on the antitrust front following last year's loss in a search advertising monopoly case. Federal Judge Leonie Brinkema of the Virginia federal court stated that Alphabet Inc. Class C intentionally controlled the open display ad server market and the ad exchange market, forming and maintaining a high degree of control in these two areas. She pointed out that Alphabet Inc. Class C imposed restrictive policies on clients, making it difficult for other advertising technology companies to compete fairly, thus consolidating its monopoly advantage. Following this news, Alphabet's stock price fell by about 1.5% in early trading on Thursday, with an intraday drop exceeding 3%. Alphabet Inc. Class C has not publicly responded to this ruling yet. However, the judgment did not entirely favor the U.S. government. The court found that the government had not sufficiently proven that the "open display ad server market" was an independent and effective market, so this charge was not proven. Nevertheless, the court has required Alphabet Inc. Class C and the government to jointly submit a set of "remedies" to address Alphabet Inc. Class C's improper behavior in the advertising market. This is another major setback for Alphabet Inc. Class C in antitrust matters. Back in August of last year, in another case, a judge ruled that Alphabet Inc. Class C maintained its dominant position in the search engine and text advertising market by entering into exclusive agreements with browser companies, smartphone manufacturers, and telecommunications carriers to prevent users from accessing other search services. Alphabet Inc. Class C has long been a leader in the global online advertising technology sector, but as regulatory scrutiny intensifies, its business model is facing increasingly more legal challenges. This new ruling could have a profound impact on Alphabet Inc. Class C's advertising business, and it signals that the U.S. government's regulatory efforts to limit the market power of tech giants are continuing to escalate.