More than 435,000 Chicago students have the day off Friday, with hundreds of schools closed due to a one-day walkout by the Chicago Teachers Union.

Teachers that don’t show up for work will not be paid by the district. If teachers do show up for work, however, they will have to give the money they earn to the union, per union rules. If they don’t pay, they may be suspended or expelled from the union. If expelled, they can keep their job but still have to pay union dues, even though they can’t vote as a union member.