A Supreme Court case that held that federal courts could hear cases that claimed that malapportionment of state legislatures violated the Equal Protection Clause of the Constitution. By holding that such cases were justiciable, the Supreme Court paved the way for federal courts (and not just state courts) to hear and decide on reapportionment issues.
Plaintiff had sought to force reapportionment of voting districts in Tennessee on the ground that unequal representation was unconstitutional; the lower courts had denied relief on the grounds of non-justiciability. The Supreme Court held that the constitutionality of legislative appointment schemes was not a political question and therefore was justiciable (i.e., the Court could hear the case and decide on the merits).
The Court delineated a series of factors, at least one of which must be present, in order for the case to be a non-justiciable political question: (a) commitment of the issue to a branch of government other than the judiciary; (b) lack of standards for resolving the issue; (c) impossibility of the judiciary to resolve the issue without first making a policy determination; (d) a judicial decision of that matter as a lack of respect for other branches of government; (e) a political decision has already been made; or (f) the potential for multiple pronouncements by various branches on one question.
Full text of Baker v. Carr (1962):