HALF MOON BAY, Calif. (AP) — A judge required a billionaire technology mogul to testify at a trial underway over public access to a popular Northern California beach.

Sun Microsystems co-founder Vinod Khosla bought the 53-acre Martin’s Beach property about 35 miles south of San Francisco in 2008 for $37.5 million and closed the only road to the site, prompting a lawsuit.

San Mateo County Judge Barbara Mallach denied a motion on the first day of the trial on Thursday that sought to spare Khosla from testifying. Khosla is scheduled to testify on Monday afternoon.

Khosla is opposed by The Surfrider Foundation, which argues that he is violating the California Coastal Act by blocking the road that leads to the beach. Under state law, the beach is open to the public, but without the road access, it can only be reached from the ocean.

Khosla’s attorney, Jeffrey Essner, says the public was previously allowed to access the beach for a fee, so there was no right of public access.

“This lawsuit represents a clash between the constitutional right of a property owner to exclude (the public) from his private property and the cause of a political and activist organization to gain access,” Essner said in court on Thursday. Essner is representing Martin’s Beach LLC, the company Khosla evidently established to purchase the beachfront land.

“Surfrider, in this lawsuit, is asking to protect an access right that simply doesn’t exist,” Essner said.

Martin’s Beach LLC painted over a billboard welcoming people to the beach, put up a locked gate and hired armed guards to keep people out, according to The Surfrider Foundation’s lawsuit.

Those steps constituted development and required a permit from the California Coastal Commission, the lawsuit says.

“This case is about compliance with the coastal act,” said Eric Buescher, who is co-counsel for Surfrider. “It’s about ensuring that violations are punished.”

California has seen other battles over public access to the coast.

In the most famous example, film and music mogul David Geffen fought for decades to block public access to the beach in front of his Malibu compound. In 2007, he finally changed course and a public easement was added to his property.