In a series of great cases the Supreme Court of the United States has laid down the doctrine that the Eleventh Amendment does not grant to States nor to their agents a power, unrestrainable by judicial process, either to interfere with the exercise of federal rights or, under color of unconstitutional legislation, to violate the private rights of individuals. Where this danger has been threatened, writs of injunction have been issued, and, for the performance by state officials of purely ministerial acts prescribed by law, mandamus has been awarded. Thus in Hans v. Louisiana28 the court, after admitting the non-suability of a State either by its own citizens or citizens of other States, took the precaution to say: " To avoid misapprehension it may be proper to add that, although the obligations of a State rest for their performance upon its honor and good faith, and cannot be made the subject of judicial cognizance unless the State consents to be sued, or comes itself into court; yet, where property or rights are enjoyed under a grant or contract made by a State, they cannot wantonly be invaded. Whilst the State cannot be compelled by suit to perform its contracts, any attempt on its part to violate property or rights acquired under the contracts, may be judicially resisted; and a law impairing the obligation of contracts under which such property or rights are held is void and powerless to affect their enjoyment."

25 9 Wh. 904 : 0 L. ed. 244.

26 11 Pet. 257: 9 L. ed. 709.

27 2 Pet. 318; 7 L. ed. 437.

Acting under the right thus declared of preventing a State, or rather the officials of a State, from .acting under laws unconstitutional, either because impairing the obligation of contracts, or taking property without due process of law the federal courts, while declaring themselves unable to secure to private individuals an enforcement of their claims against States, have nevertheless been able to extend their protecting power to prevent the States from taking action upon their part to enforce against individuals and against its federal officials claims not supported by valid laws.

The following are instances illustrating this: