Google stated on Wednesday that it provides an open operating system in which clients are free to download apps directly from developers’ websites.

Three dozen states and the District of Columbia filed an antitrust suit against Alphabet Inc.’s Google on Wednesday, alleging that the company operates an illegal monopoly with its Google Play app store.

The bipartisan antitrust suit adds to the company’s mounting legal challenges. Led by the state of Utah and filed in the US District Court for the Northern District of California, it alleges that the company has monopolized the distribution of apps on mobile devices that run the Google-owned Android operating system, shutting off competition through contracts, technical barriers, and other means.

In a blog post, Google stated that it provides an open operating system in which clients are free to download apps directly from developers’ websites.

“It’s strange that a group of state attorneys general decided to file a lawsuit against a system that provides more fairness and choice than others,” wrote Wilson White, senior director of public policy.