MOSCOW, Oct 27 (Reuters) - Russia has opened an antitrust case against Apple (AAPL.O) for failing to allow app developers to tell customers about alternative payment options when using its App Store platform, Russia"s anti-monopoly regulator said on Wednesday. The U.S. tech giant could face a fine based on its revenue in Russia if found guilty of a breach, the regulator said. It did not indicate the size of any potential fine.The company was earlier issued with a warning over the issue and given a Sept. 30 deadline to "stop abuse on the market", the Roskomnadzor regulator said in a statement. Apple did not immediately respond to a Reuters request for comment. Russia has stepped up a long-running crackdown on U.S. tech giants this year in a push to expand its sovereignty over the internet in Russia. Apple faced pushback over its App Store rules in the United States last month when a federal judge issued a ruling forcing the company to allow developers to send their users to other payment systems. read more