Congress created the United States Tax Court to hear grievances over certain actions taken by the Internal Revenue Service (IRS), but has fixed time limits for taxpayers to file petitions depending on the issue they seek to have reviewed. Unfortunately, taxpayers sometimes miss these deadlines, giving rise to litigation over whether the congressionally imposed time limit is jurisdictional, in which case the Tax Court is barred from reviewing the IRS's action, or a "claims-processing" rule, in which case the Tax Court can apply equitable principles in deciding whether to reach the merits of the petition.