BRECKENRIDGE, Colo. (AP) — A tourism-dependent area in Colorado’s mountains has reinstituted a mask mandate because of a growing number of COVID-19 cases.

Starting Thursday, people will have to wear masks in public indoor spaces in Summit County, home to several ski resorts.

In a press release, the county’s public health department said the decision was made in response to an “alarming” increase in cases during the past week. Officials believe that’s due to the spread of the highly contagious Omicron variant, likely at indoor holiday gatherings.

The county has among the highest incidence rates in the United States, as does the Aspen area.

Summit County leaders had been reluctant to re-impose a mask mandate partly because it would put service workers in the difficult position of enforcing it, the Summit Daily reported. However, they were also concerned about the number of workers who have had to quarantine and saw the move as a way to help businesses.

“To me, it’s just a really commonsense approach and something we need to take to help mitigate this, even if it’s minuscule in what it does,” county commissioner Elisabeth Lawrence said. “It also provides a level of comfort for our locals.”

On Tuesday, Denver extended its latest mask mandate through Feb. 3.