Over the last few months, University of California officials have boasted that they have admitted the most racially diverse class ever to their sprawling system.

They have managed to do this, they say, despite a 28-year-old state ban on considering race in college admissions, known as Proposition 209.

But a lawsuit filed on Monday by a newly formed group takes aim at the university’s efforts, accusing the California system of cheating by secretly restoring race-conscious admissions in defiance of the state law. The group, Students Against Racial Discrimination, was organized by a persistent critic of affirmative action.

The lawsuit accuses the California system of harming all students by gradually bringing back racial preferences in recent years to stem public outrage over the low number of Black and Hispanic students at the state’s top universities.

Stett Holbrook, a spokesman for the University of California system, said the university had not yet been served with the legal papers, so it could not reply directly to the lawsuit. But he said that after the ban, it had adjusted its admissions practices to comply with the law, and it collected undergraduate students’ race and ethnicity for statistical purposes only, not for admission.

Students Against Racial Discrimination was founded last fall by a group that includes researchers and Asian American anti-affirmative action activists. Among them is Richard Sander, a law professor at the University of California, Los Angeles, who has made something of a crusade of fighting affirmative action.