Free speech advocates are expressing concern that instructions from University of Missouri police on how students should report "hateful and/or hurtful" speech could stifle legitimate differences of opinion.

A campus email sent Tuesday instructs recipients to call university police as soon as possible and notes that while such speech isn't always illegal, students can nonetheless be punished by the Office of Student Conduct.

The university's student conduct code prohibits harassment, which it defines as "unwelcome verbal or physical conduct" against "actual or perceived membership in a protected class ... that creates a hostile environment." The conduct code also forbids bullying, retaliation and threatening or intimidating behaviors.

The American Civil Liberties Union of Missouri responded with a statement calling for the university to not compromise the right to free expression in its efforts to fight racism. Its statement says, "Mistakenly addressing symptoms — instead of causes — and doing it in a way that runs counter to the First Amendment is not the wise or appropriate response."

A University of Missouri police official referred questions about the email to the school's media relations office, which did not immediately respond.

The school's email spurred a libertarian-leaning student group, Young Americans for Liberty, to set up a "free speech wall" in a campus walkway Wednesday. The chapter's president, Ian Paris, said school administrators seem intent on quelling free speech, and members encouraged passers-by to write whatever they wanted on the large strip of paper.

"Basically, if your feelings are hurt the police are going to crack down on whoever hurt your feelings," Paris said. "I think that's terrifying, because I have opinions every single day that people find offensive or hurt their feelings because I disagree with them."

Authorities on Wednesday arrested a 19-year-old student at another Missouri campus, alleging he posted online threats about shooting black people on the Columbia campus. The threats were posted Tuesday, a day after the university system president and the chancellor of the Columbia campus announced they were resigning amid student-led protests over their handling of racial issues.