Russia's Federal Antimonopoly Service found that Google and the Irish subsidiary through which it contracts with customers outside the U.S. abused their market dominance.
The antitrust authority opened the case in February following a complaint from Russian search engine Yandex, which also develops mobile apps and runs its own Android app store.
Late Monday, the authority said Google had broken Russian law by requiring phone makers to install its own app store, applications and search system on Android phones intended for sale in the Russian Federation, and to place its apps on the devices' home screen.
That requirement had the effect of preventing developers of competing services from having their apps installed by the vendors, the authority said.
Under Russian law, Google could face a fine of up to 15 percent of its revenue from selling goods and services in the market where the offense was committed.
The authority will draft a full decision within two weeks, requiring Google to stop abusing its market dominance and imposing further remedies to support competition. Those remedies could include removing the contract clauses that prevent phone manufacturers from installing apps and services that compete with Google's, and are likely to be imposed from October, it said.
The authority closed another investigation into whether Google had engaged in unfair competition, saying it had found no evidence of violations of that aspect of Russian law.