The students want President Milton Gordon to sign what they call the "Declaration to Defend Public Education," a statement from students and faculty protesting budget cuts in the university system.
The president did not sign the statement, citing concerns about some of the language regarding teachers.
"It's a completely symbolic signature. It's just an act of good faith from our administration, and he won't give that to us," said student Carie Rael. "He won't show his support. He says he's supportive. He states all these statistics on how he's supportive, but we don't see that."
The sit-in started around 9 p.m. Monday after a meeting between students and the university's president. Dozens of students spent the night on the floor of the administration building.
The Cal State Fullerton students were joined by students from Cal State Dominguez Hills on Monday night, and they are expecting students from several other schools to join them on Tuesday.
"Historically, the CSU has been the affordable college system, and now it's not getting that way, and it's becoming a privilege and it's not a right anymore," said student Tamara Khoury. "And I myself am struggling to even pay tuition."
On Tuesday, the vice president of student affairs, Sy Abrego, met with the demonstrators.
"If we can separate the issues, I think that the university as a system is all concerned with higher education, the funding of higher education, so we share the same concerns that the students have," Abrego said.
Student Bryan Norton said they are willing to work with school officials, but they want the president to be there.
"We know that they do have individual opinions that do differ from the president's, and we want everything on the table," he said.