A federal judge has sided with the City of San Francisco, saying that San Francisco International Airport's trademark is likely being infringed upon by Oakland Airport's new name, which was chosen by the Port of Oakland's board this spring.

San Francisco filed for a preliminary injunction in September, ahead of a final ruling, to stop Oakland Airport from referring to and marketing itself as San Francisco Bay Oakland International Airport. And on Tuesday, as the Chronicle was first to report, U.S. Magistrate Judge Thomas Hixson issued a ruling granting that injunction.

"As a result of San Francisco's marketing efforts and the recognitions SFO has received for its services, the name and trademark San Francisco International Airport is widely known among air travelers and within the travel industry," Hixson writes in the ruling, adding that the city "has spent many millions of dollars to develop a brand" for SFO, and has a right to protect it.

While Hixson does not rule on the issue of whether air travelers have already been confused by Oakland's name change — something that the City of San Francisco presented some scant evidence of — he seems to say that doesn't matter, and that Oakland is likely to lose the battle in a final ruling on trademark infringement.

Hixson writes that travelers could be "confused into thinking that OAK is a branch or division of [SFO], or that SFO and OAK have the same management or ownership." He then provides a humorous analogy: "Suppose you founded an amusement park in North Dakota, and you named it the Disney North Dakota Amusement Park. Customers who go to that park understand they are in North Dakota and therefore not at Disney World in Florida or Disneyland in California. The claimed confusion would be that using the word 'Disney' in the name of the park implies an affiliation that is untrue."

So, even if a traveler was never confused about the fact that they were headed to Oakland and not San Francisco, the name change "is highly likely to imply affiliation, connection or association to the typical airline customer."

He also includes a dis for Oakland Airport, suggesting it is trying to borrow some prestige from SFO. "The San Francisco International Airport brand is routinely ranked among the top airport brands,” Hixson writes. “By contrast, the Oakland airport is much smaller than SFO, with more limited infrastructure, and far fewer flights. It is rated worse in terms of customer satisfaction. The new name for the Oakland airport strongly implies affiliation with San Francisco and the San Francisco International Airport."

This may not be the last word on the matter, and a final ruling is still pending. But Oakland Airport is now ordered to remove any new signage or branding with the new name, pending that final decision. And, Hixson says, this shouldn't be any great harm to the Port of Oakland since "it remains free to use the well-known name for the Oakland airport that it has used for 60 years."

Previously: Oakland Airport Hits Back on SFO Injunction, Claims SFO 'Manipulated Results’ Showing People Went to Wrong Airport