Which of the following is NOT a requirement for S Corporation status?

An S Corporation must meet specific requirements to maintain its status under the Internal Revenue Code. Among these requirements, all shareholders indeed must be individuals or qualifying trusts and estates, with restrictions on certain entities. This includes that shareholders cannot be partnerships or other corporations, which means that partnerships or corporations cannot hold shares in the S Corporation.

Having U.S. citizens or certain eligible residents as shareholders helps ensure compliance with the intentions of the S corporation structure, which is aimed at closely-held businesses with fewer formalities than C Corporations. Thus, stating that "all shareholders must be U.S. citizens" is misleading because it fails to capture eligible residents, such as green card holders.

In terms of the other requirements, being limited to a maximum of 100 shareholders and having only one class of stock are essential criteria for the formation and operation of an S Corporation. Therefore, these elements are crucial for establishing and maintaining S Corporation status.