Updated

Penn State president Rodney Erickson is admonishing students who wore costumes and held offensive signs in photographs circulated on the Internet.

But Erickson said in a campus-wide letter Thursday that the school won't pursue disciplinary action. He said the behavior was protected by free speech rights.

His letter didn't specifically reference the photos or name the Chi Omega sorority. But Erickson said it became clear recently that some students "celebrated Halloween in costumes that offended others" and acted contrary to university values.

One sign in the photo of sorority sisters says "will mow lawn for weed + beer." Two women holding signs are wearing fake mustaches. Others in the photo are wearing sombreros.

The sorority has apologized. Chi Omega's national chapter says it is placing the sorority on probation.