An exercise of the Spending Power with conditions (strings attached) is valid if:

(1) the spending program is in pursuit of the general welfare (courts generally defer to Congress in defining general welfare);
(2) any condition it includes is unambiguously stated so that the states can make a knowing choice;
(3) there is a relationship between the condition imposed and the purpose of the federal spending;
(4) the condition does not induce the states to violate some other provision of the Constitution and, therefore, be independently barred (consider this issue by asking whether a state could enact the condition on its own, in the absence of the incentive of a federal spending program, without violating the constitution); and
(5) the financial inducement offered by Congress must not be so coercive as to go beyond pressure and amount to a compulsion.

Note: The above test is consistent with the view of at least one lower court which has interpreted South Dakota v. Dole as imposing the following five restrictions on Congressional power to attach conditions to exercises of its spending power:

(1) The exercise of the spending power must be for the general welfare;
(2) The conditions must be stated unambiguously;
(3) The conditions must bear some relationship to the purpose of the federal spending;
(4) The conditions for the expenditures must not violate some other constitutional command; and
(5) The financial inducement offered by Congress must not be so coercive as to pass the point at which pressure becomes compulsion.

See Constantine v. George Mason University, 411 F.3d 474 (4th Cir. 2005).