The Golden State Warriors' plans for a new arena in San Francisco are suddenly being met with opposition.

An anonymous group of what organizers describe as wealthy donors to UCSF hired an imposing cast of consultants — including former UCSF Senior Vice Chancellor Bruce Spaulding and, for a time, former Mayor Willie Brown to block the Warriors' plans for an arena in Mission Bay near the waterfront.

“This arena is going to essentially ruin decades of good work and planning in Mission Bay and make it impossible for people to access the hospital there,” said public relations pro Sam Singer, who has also been hired by the antiarena forces.

Along with the arena, the project would include two 160-foot-tall office buildings and a central plaza larger than Union Square.

The Warriors plan to build just 950 parking spaces for the project, 650 of which would serve the two office towers.

The opponents have formed Mission Bay Alliance, a nonprofit whose contributors are allowed to remain anonymous.