After a surge of coronavirus cases at the University of Colorado-Boulder, health officials on Thursday announced a ban on gatherings for 18 to 22-year-olds.

“We must take stronger action to stop the spread of this virus in our community,” Boulder County public health director Jeff Zayach said in a news release. “We have researched the actions we can take that would be effective while minimizing the burden on those who have not been the source of increased transmission. We believe this strategy can achieve both goals.”

The ban began on Thursday at 4 p.m. local time.

The ban comes after students repeatedly violated public health orders. Those who violate the order can be fined up to $5,000 and sentenced up to 18 months in jail.

Phil DiStefano, the Chancellor of the University of Colorado-Boulder, sent a letter Thursday to the university saying that the school is trying to enhance its access to health and wellness services.

Students have the option to stay on campus and follow public health guidelines, or to return home and fully transition to remote learning.

However, DiStefano urged students to stay and wrote in the letter “traveling home is not our preference and public health agencies have advised against it.”

“Like many of our peer universities across the country, we continue to face new challenges related to the COVID-19 pandemic. Some have enacted similar approaches to ours and are successfully reducing their positive cases,” DiStefano said.

The Boulder County Public Health Department first noticed an upward trend in new COVID-19 cases on Aug. 24, the first day the university started physical classes.

Out of 1,469 confirmed or probable cases, 1,097 were affiliated with the school during that time window. That's nearly 80% of Boulder’s COVID-19 cases.

On Sept. 15, the Boulder public health department asked students to quarantine for two weeks.

The following week, in-person classes were suspended until at least Oct. 7 after the initial uptick in COVID-19 cases.