A rally to support immigrants' rights in downtown Denver is expected to clog streets and may draw at least as many people who attended a march on March 25th.
That event drew at least 50,000 people, including many legal residents and citizens.
While Denver police are bracing for the thousands, similar but smaller rallies are planned across the state.
From Alamosa to Greeley, from Grand Junction to Fort Morgan, schools, restaurants and other businesses plan to run with skeleton crews or to shut down for at least part of the day.
School officials across Colorado say they'll encourage students to stay in class, but try to ensure their safety if they leave.
Meanwhile, thousands across the country are expected to call for a U.S. guest-worker program and to demonstrate the economic power immigrants have by walking out of work and declining to shop.