In Babka v. Babka, 234 Neb. 674, 452 N.W.2d 286 (1990), the Court held that a change in federal tax law constituted a material change of circumstances which would justify modification of a support order. In Babka, the parties agreed that the noncustodial parent would claim the children as dependents on his income tax returns, but this agreement was not made a part of the decree when they divorced in 1980. In 1984, Congress amended the tax code to give the deductions automatically to the custodial parent, unless the custodial parent signed a written waiver. In 1987, the custodial parent in Babka claimed the children as deductions on her returns, although she had signed the waivers in 1985 and 1986. The court ordered the custodial parent to sign the waiver, finding that the change in the tax law and the mother's refusal to sign the waiver constituted a material change of circumstances justifying the modification.