Tax World Is Nervous as Court Arguments in Moore Case Approach

The Supreme Court is set to hear oral arguments Tuesday in a critical tax-law case that is poised to create upheaval—on the federal and state levels alike.

The case, Moore v. United States, concerns whether a tax on companies’ past foreign earnings is constitutional, and whether income that hasn’t been “realized” by taxpayers can be taxed. If the court ultimately decides the answer is no, many observers fear that could trigger not only gigantic tax refunds to multinational companies, but could also preclude any future attempts to impose taxes on wealth, and call into question a host of other ...