Russia's anti-monopoly watchdog has accused Google of abusing its dominant position in the market by requiring phone-makers to pre-install its apps on Android phones.
The firm could face penalties of up to 15% of its 2014 revenue in Russia.
The case was originally launched by Russian rival Yandex in February and comes as the EU also investigates Google's Android operating system.
Google said that it was considering its next move.
"We haven't yet received the ruling. When we do, we will study it and determine our next steps," a spokeswoman told the BBC.
In Russia, Google is less dominant in search than in other European countries with rival Yandex commanding 60% of the search market.
However, the Android operating system is on more than 80% of smartphones sold in the country.
Shares in Yandex rose on the news.
Russia's Federal Antimonopoly Service (FAS) said it would be sending its full ruling to Google in the next 10 days requesting that it "terminate abuse of dominant position".
Among the original complaints against Google were:
- that it bundled apps from its mobile service with the Google Play store
- required the pre-instalment of the Google search engine by default
- required Google app icons to have preferential placement on the first screen
Yandex welcomed the ruling.
"We believe the FAS decision will serve to restore competition in the market," the company said.
In April, EU competition commissioner Margrethe Vestager began formal legal proceedings against Google over accusations that the firm's promotion of its own shopping links amounted to an abuse of its dominance in search.
The firm said it "strongly disagreed" with the allegations.
Ms Vestager also revealed that she had launched an investigation into whether the way Google bundled apps and services for its Android operating system was unfair.
It is the culmination of a five-year investigation into the company. It could ultimately lead to fines of billions of euros.