A recent Illinois Supreme Court case upheld a will provision which disinherited descendants if they did not marry a fellow Jew.
As in this case, most American jurisdictions follow the general rule that a testator, or one writing the will, has (almost) free reign to dictate how their assets are disposed of upon their death. However, most jurisdictions limit this free reign by allowing courts to strike provisions that are "against public policy". That was the argument in the Illinois case. The descendants argued that the provision amounted to religious intolerance, which they argued is against public policy. The Court demonstrated just how much leeway a testator can be given, stating that the Court was not in a position to ensure that a grandparent treats "grandchildren who reject his religious beliefs and customs in the same manner as he treats those who conform to his traditions".
Minnesota courts have not spoken on whether such religious clauses would be upheld. However, two cases give guidance on how a Minnesota court might evaluate a questionable clause. In its 2008 ruling, In re The Estate of Peka, the Minnesota Court of Appeals upheld a provision that prohibited an ex-wife from living in the testator's house, which was placed in trust for the benefit of the parties' minor child, rejecting an argument that the provision was against public policy in promoting separation between parent and child.
The Minnesota Supreme Court, all the way back in 1897, showed that they are willing to strike down a provision as being against public policy. In Morse v. Blood, the testator stated in his will that his spouse would inherit his estate, but that she would be prevented from giving, either during her life or through her will, "one cent" to either her relatives or his. Among the issues created by this clause, the Court pointed out that if the spouse invited her family over for dinner, she would run the risk that the entire estate would be forfeited. The Court called the provision "mischievous and technical" and struck it down as against public policy.
If you're thinking of putting a ... creative... provision into your will or trust. Remember that, although you will enjoy a certain amount of leeway, you run the risk that a court could strike the provision. Make sure that you meet with a licensed attorney who can draft the provision, which could increase the chances that it would later be upheld by a court.