More than half the states in the nation now have right-to-work laws in place. Wisconsin was one of the more recent states to enact such legislation, and, as often is the case, it was met with much resistance by labor unions, including judicial challenges. A federal lawsuit filed by affiliates of the International Union of Operating Engineers (IUOE) arguing that the law, among other things, violated the U.S. Constitution was struck down by a Wisconsin federal district court in September 2016. That decision was upheld on July 12 by an appeals court. The U.S. Court of Appeals for the Seventh Circuit affirmed the lower court’s ruling, expressly citing its 2014 decision voiding a similar challenge by unions against Indiana's right-to-work law. Wisconsin is thus the latest state to successfully defend this type of legislation in court. Right-to-work laws are permitted under Section 14(b) of the Taft-Hartley Act, and they make it unlawful for companies to require union dues as a condition of employment. In states where right-to-work laws are not enacted, most unionized employers have clauses in their labor agreements that require dues payments as a condition of employment – the clauses generally are known as "union seniority clauses." At present, 28 states have right-to-work laws on the books. The National Right to Work Foundation maintains a current list.