A Supreme Court decision striking down the federal ban on gay marriage would bring dramatic changes to the financial lives of the country's 120,000 married same-sex couples. On Friday, the court announced it will hear a case challenging the Defense of Marriage Act -- a 1996 law known as DOMA that defines marriage as between a man and a woman. If DOMA is found unconstitutional, same-sex couples married at the state level will become eligible for the same federal treatment as opposite-sex couples when it comes to financial matters like taxes and Social Security benefits. The court's ruling is expected by the end of June. The justices also took up Proposition 8, a California measure banning gay marriage in the state. Gay marriage is legal in nine states and Washington, D.C. More than nine other states grant civil unions or domestic partnerships, but couples in those states are unlikely to be impacted, said Judi O'Kelley, deputy director of development at nonprofit Lambda Legal.