SAN FRANCISCO — After facing allegations from Uber that it nurtured online advertising fraud to extract millions of dollars, the global advertising firm Fetch Media Ltd. has fired back with a new lawsuit that accuses Uber of forum-shopping and evading its bills.

Uber Technologies Inc. sued Fetch in September for $50 million claiming it was charged for mobile ads by Fetch that never generated returns. The lawsuit landed in front of U.S. District Judge Yvonne Gonzalez Rogers of the Northern District of California.