As expected, opponents of the Golden State Warriors arena approved for San Francisco’s Mission Bay have filed the first in what could be several lawsuits to derail the $1 billion project.

The suit filed late Thursday afternoon charges that UCSF Chancellor Sam Hawgood overstepped his authority by signing a memorandum in support of the project in exchange for transportation improvements pledged by the city of San Francisco. In doing so, says the complaint filed in Alameda County Superior Court, Hawgood tied the hands of University of California without the approval of the system’s Board of Regents.

“California law imposes careful limits on leaders like Chancellor Hawgood and others,” the attorney representing the opponents, Josh Schiller of the firm Boies, Schiller and Flexner, said in a statement released after the suit was filed. “The chancellor can’t give away UCSF’s valuable property rights, which belong to all Californians.”

The basketball team’s 18,500-seat home would be located off Third Street in the Mission Bay district, one block from the huge UCSF medical center that opened early this year. There has been little political opposition to the proposed development, which received votes of approval this month from the Board of Supervisors, but several large UCSF Mission Bay donors have said the sports and event complex could cause dangerous gridlock.

The suit was filed in the name of the opposition group, the Mission Bay Alliance, as well as their consultant Bruce Spaulding and Jennifer Wade, the mother of a child who receives treatments at the children’s hospital in the medical center.

A UCSF representative declined to comment on the complaint because the school has yet to receive a copy. Warriors spokesman P.J. Johnston ridiculed the move and pointed out that the opposition campaign’s funders, the alliance, have not identified their members.

“This super PAC came in claiming to represent the interests of UCSF,” Johnston said in a statement. “This attack shows they’re only serving their own interests — and they’re willing to damage UCSF in the process.”

The threat of lawsuits has been part of the antiarena case from the start, and legal challenges to the environmental impact report are expected as well. Team officials have said that they intend to have the arena up and running for the 2018-19 season. The project will also include two office buildings and a public plaza.

John King is a San Francisco Chronicle staff writer. E-mail: jking@sfchronicle.com Twitter: @johnkingsfchron