SAN FRANCISCO — Uber Technologies Inc. has sued global advertising firm Fetch Media Ltd. for $50 million claiming it was charged millions for mobile ads that never generated returns.

The lawsuit, filed Monday in U.S. District Court for the Northern District of California by Uber’s lawyers at Reed Smith, shines a light on some of the issues dogging the advertising industry in the digital age, as well as just how much money Uber spends to get new users to download its ride-sharing app.