More than thirty US states initiated an antitrust lawsuit against Google on Thursday in the US District Court for the District of Columbia. The lawsuit alleges that Google has abused its position as a “Silicon Valley titan” by manipulating its search results to dominate its smaller rivals.

The issue arose in October when the US Department of Justice filed suit against the search and search advertising company. The agency accused Google of entering into deals with other technology giants to protect its monopoly and suppress competition illegally. The Thursday lawsuit was brought by a bipartisan group of state prosecutors one day after ten other states alleged that Google abused “its dominance in advertising” and overcharged publishers.

The forty states claim that Google has solidified its monopoly in search using a variety of anti-competitive tactics. Among the most notable tactics, the company is alleged to control search results to turn out its own products and services. This strategy reputedly prevents internet users from seeing the best options when searching on the web. The prosecutors also asserted that one of the chief anti-competitive tactics that Google uses involves special deals the search engine company signs. These deals are signed with phone makers like Apple to ensure that Google is the default option on internet browsers, smartphones, and other connected devices.

The stifling of competition, state attorneys general alleged, has established Google’s nearly 90 percent market dominance in search and search advertising. Phil Weiser, the Democratic attorney general of Colorado, stated: “Google’s anti-competitive actions have protected its general search monopolies and excluded rivals, depriving consumers of the benefits of competitive choices, forestalling innovation, and undermining new entry or expansion.”

Google responded to the lawsuit by state attorneys general in a blog post authored by Adam Cohen, the company’s director of economic policy. Cohen asserted that the Google search design has evolved to deliver more useful information to users, not stifle competition. He further argued that changing the search giant’s business practices would harm the quality of search results. “We look forward to making that case in court,” Cohen wrote.