Union Bank of California has kicked off a legal battle to prevent Zions Bancorp. from using the name Bank of California.

In a lawsuit filed last week in U.S. District Court for the Central District of California, Union Bank said it still owns the trademark that Zions said it plans to adopt in the Golden State.

Bank of California, a venerable name in the state, was in use until its last owner, Mitsubishi Bank Ltd., merged in 1996 with Union Bank of California's parent, Bank of Tokyo Ltd.

According to the legal complaint, the U.S. Patent and Trademark Office renewed Union Bank of California's rights to the name in September 1988.

Union Bank said it believes the trademark is worth $1 million.

"We still use it," said Michael T. Connell, senior vice president and associate general counsel of Union Bank. "We use it in marketing material, and it is etched in granite on our 400 California Street building" in San Francisco.

Zions said May 29 it would use the name to unify three acquisitions: $720 million-asset Grossmont Bank of San Diego; $350 million-asset Pacific National Bank, Escondido; and $5 billion-asset Sumitomo Bank of California, San Francisco.

Zions, which is based in Salt Lake City, said it settled on "Bank of California" after polling 800 employees of these banks.

Union Bank is claiming use of that name would cause it "irreparable injury ... including injury to its reputation and dilution of the distinctive high quality of its mark."

"A lot of goodwill has been built up with that name," Mr. Connell said. "The middle-market business segment we serve has come to identify with the Bank of California name."

A Zions official, speaking on condition of anonymity, said, "Based upon the advice of legal counsel and on other investigations and inquiries, we believe that the name Bank of California is available."

But because of the suit, the official added, "We are having the issue reviewed by attorneys."

The dispute will not necessarily end up in court. Mr. Connell said his bank hopes to arrive at an "amicable solution"-which he said would involve Zions' dropping of the coveted name.

Subscribe Now

Access to authoritative analysis and perspective and our data-driven report series.

14-Day Free Trial

No credit card required. Complete access to articles, breaking news and industry data.