Las Vegas (CNN) National Nurses United, the largest nurses union in the country, will march and rally for Bernie Sanders outside of Tuesday's Democratic debate in Las Vegas.

Promising a "colorful" rally, the nurses and union organizers will march from the nearby Treasure Island Hotel to the debate site at the Wynn Las Vegas. The event is supposed to be a show of force for Sanders, a candidate the union endorsed in August.

Organizers said they expect "a couple hundred" people to attend the rally.

When National Nurses United endorsed Sanders -- over former secretary of state Hillary Clinton -- in August, they became the first national union to back the independent Vermont senator.

Read More