Fraternities at the University of Colorado Boulder have been banned from writing in chalk on campus sidewalks because they aren't university-affiliated student groups.

The Daily Camera reports that fraternities in Boulder have been independent from the university for more than a decade, so when brothers chalked messages encouraging students to attend rush events they were met with threats of the student conduct office.

The university announced in October that it would attempt to re-establish ties with fraternities, but existing organizations have been unwilling to lose their independence. At least one new chapter has backed out of affiliating with the university.

Fraternity officials say they should be able to communicate with their classmates and that they worry the chalk policies are retaliation for not re-joining the school.

University officials say they are only enforcing the rules.