LOS ANGELES (Reuters) - Students and rights groups plan to demonstrate at Stanford University’s commencement on Sunday to express outrage over the 6-month jail sentence handed to a former student convicted of sexual assault on the California campus, organizers said on Saturday.

Activists hold signs calling for the removal of Judge Aaron Persky from the bench after his controversial sentencing in the Stanford rape case, in San Francisco, California, U.S. June 10, 2016. REUTERS/Stephen Lam

UltraViolet, a women’s rights group, said it commissioned a plane to fly over Stanford’s Palo Alto campus just ahead of graduation ceremonies with a banner reading, “Protect Survivors. Not Rapists. #PerskyMustGo.”

The tag refers to Santa Clara Superior Court Judge Aaron Persky, who handed down what many consider to be an extraordinarily light sentence against former Stanford student-athlete Brock Turner, 20, for his conviction in a 2015 sexual assault.

In addition, Stanford students said on social media that they planned to carry protest signs as they walk toward the prestigious university’s commencement.

Protest organizers from UltraViolet have said online they want to see members of the Stanford community speak out against the sentence. The aim is to strike a blow against a culture on college campuses that they say discourages victims of sexual assault from coming forward.

Turner’s sentencing on June 2 gained international attention after a detailed letter that the victim had read aloud in court was posted online. It describes the devastation the woman felt in being sexual assaulted while unconscious after partying.

A Stanford law professor is leading a signature-gathering drive to remove the judge from office for handing down the six-month sentence even though prosecutors had recommended six years.

Santa Clara County Assistant District Attorney James Gibbons-Shapiro told the San Jose Mercury News that his office does not have a legal basis to appeal the sentence because the judge was authorized by law to mete out the sentence he gave.

Some students have said on social media they would protest at “wacky walk,” a Stanford tradition where students in costumes hold celebratory signs as they head toward graduation ceremonies, where documentary filmmaker Ken Burns is scheduled to be the keynote speaker.

Persky is legally unable to comment on the case because Turner is appealing his conviction, Santa Clara County court spokesman Joseph Macaluso has said.

Some media commentators have pushed back against criticism of Persky. At Slate.com, legal writer Mark Joseph Stern this week described the sentence as too lenient, but wrote that recall efforts against Persky threaten judicial independence.