The California State University system amassed a surplus of more than $1.5 billion over 10 years, hiding it from students and the public even as the trustees doubled tuition to nearly $6,000 and collected rising amounts of state funding, the state’s independent auditor said Thursday.

The university “did not disclose the surplus to students when consulting with them about raising tuition costs,” or in financial disclosures to the Legislature, Auditor Elaine Howle said in the report, which covered 2008 to 2018. She noted that by withholding the news of the hefty surplus — most of which came from student tuition — CSU undermined the state law that requires public universities to discuss tuition plans with students before raising prices.

“Had CSU informed the legislators of its surplus when presenting its budget requests, the legislators could have directed CSU to use a portion of its own money rather than requesting additional funding from the state,” Howle wrote, adding that an example of how CSU could use the money would be “offering additional courses to help students graduate more quickly.”

CSU Chancellor Timothy White rebutted the audit findings and defended the university’s financial disclosure practices. He said the $1.5 billion is a legitimate part of CSU reserves used to pay short-term expenses, such as debt service and campus maintenance, and for economic uncertainty.

“I fundamentally disagree with the assertion in the audit report that this is a surplus and that it’s discretionary money,” White told The Chronicle. “It is not a surplus. We cannot use it for ongoing costs.”

The findings are similar to those in a 2017 audit involving the University of California’s Office of the President, in which Howle revealed that President Janet Napolitano had socked away $175 million for use on her preferred UC projects while failing to disclose the funds to the regents as they demanded more money from the state. Those audit findings led to state hearings, changes in state law and, ultimately, a public apology from Napolitano for her role in interfering with the auditor’s work.

The audit of CSU — with 23 campuses and about 480,000 students — focuses on a vastly greater sum of money, but different circumstances.

In UC’s case, the president’s office collected money from its 10 campuses as a tax to operate the UC system. The audit found the president’s office siphoned off money for private projects — from addressing student hunger and restoring wetlands, to hosting extravagant parties for retiring regents.

In CSU’s case, the $1.5 billion — largely student tuition — is part of $4 billion held in an investment account that CSU calls its reserve funds. But the auditor says the $1.5 billion is discretionary money that CSU could use for instructional purposes, and that despite submitting numerous financial documents to the state, CSU “did not provide the detail necessary for the Legislature to easily understand” that this portion of the reserves was actually surplus funding.

CSU issued a statement declaring the university “transparent in its financial operations” and said that detailed information about its money “is readily available for review by Californians and our state’s lawmakers.” White said he always has been up-front with students about CSU finances.

On Thursday, the president of the Cal State Student Association disagreed.

“It is disappointing and concerning that the CSU did not disclose their reserve amounts during their required consultation with students regarding tuition increases,” the president, Mia Kagianas, a business major who just graduated from Sacramento State, said in a statement. “Students deserve accessible information on the institution’s budget in decision-making processes that directly impact their lives.”

Kagianas called alarming a separate audit finding released Thursday, that the price of student parking soared at four CSU campuses even as parking remained hard to find.

Howle’s audit found that the four campuses audited by her team — Sacramento, San Diego, Fullerton and Channel Islands — raised student parking fees from 24% to 64% during the 10 years studied, and now charge annual fees from $336 (San Diego), to $472 (Fullerton). The campuses also failed to develop alternative transportation options, such as shuttles and carpools, or to facilitate cycling, the audit found.

White acknowledged that at the campuses, “there is no doubt that people are frustrated by parking problems” because student enrollment has risen faster than the number of parking spots.

Students pay for “more of a hunting license than a parking license,” he joked, adding that prices have risen because it costs more to maintain the facilities. At the same time, he said, the campuses “should do better in disclosing their alternative transportation” options before proposing new garages.

Leaders of the California State University Employees Union, which represents thousands of support staff across the system, proposed the audit last year to Assemblywoman Sharon Quirk-Silva, D-Fullerton (Orange County).

The employees, who were in contract negotiations with CSU, “were concerned about the cost of parking” and the progress of their labor dispute, said Quirk-Silva, who served on the Higher Education Committee and requested the audit.

“I’m surprised” at the size of the discretionary funds, she said Thursday. “That’s $1.5 billion that could have been used to not raise tuition in 2017-18, and for additional student support.”

CSU raised tuition that year by $270, to $5,742, excluding mandatory fees that boost the price above $7,000.

State funding for CSU grew by about 60% from 2013 to 2018 — from about $2 billion to $3.2 billion — even as CSU’s surplus nearly doubled in size, the audit found.

“For years, CSU has claimed poverty, and now we find they’ve been holding $1.5 billion,” said Neil Jacklin, the union’s president. “This is just the latest example of CSU leadership irresponsibly managing public funds.”

In the CSU statement, White said he is concerned that the audit findings would mislead the public.

“The report’s incorrect claim that CSU failed to fully inform its stakeholders about fund balances overlooks dozens of presentations of publicly available reports that included information about these funds,” White said, adding that calling the $1.5 billion a “discretionary surplus” mischaracterizes how CSU is able to use the money.

Nanette Asimov is a San Francisco Chronicle staff writer. Email: nasimov@sfchronicle.com Twitter: @NanetteAsimov