Which legislative action is required for admitting a new state into the Union?

To admit a new state into the Union, a simple majority vote in Congress is required. This process begins with the prospective state applying for admission, followed by Congress passing an admission act. The U.S. Constitution provides the framework for this process, allowing Congress to determine the admission procedure for new states. A simple majority in both the House of Representatives and the Senate is necessary for the admission act to move forward.

Other options involve processes that aren't relevant to the admission of new states. For instance, a constitutional amendment is not needed to admit a new state, since the Constitution allows for the admission of states through legislation. Moreover, a presidential signature alone does not suffice, as Congress must first approve the admission. Additionally, a state referendum is not typically part of the process; the decision is made at the federal level by Congress, and while local approval might be considered, it is not a formal requirement for statehood. Thus, the requirement for a simple majority vote clearly outlines the constitutional procedure for admitting new states.