WASHINGTON, DC — On Friday, the U.S. Supreme Court stepped into the charged debate over same-sex marriage by agreeing to review two court challenges to federal and state legislation that restricts the legal definition of marriage to the union between a man and a woman.

The justices announced that they would not only review the Defense of Marriage Act (DOMA), the law that denies married gay couples the same federal benefits received by heterosexual couples, but that they will also consider the challenge to California’s Proposition 8, the state law that prohibits gay marriage which was narrowly approved by voters in 2008.

The announcement of the second review came as a surprise to many experts.

Both supporters and opponents of marriage equality say they are optimistic about the outcome of the justices’ ruling.

The high court is expected to hear arguments in the two cases as early as March, with a decision to come by the end of June.

In 31 states, voters or state legislatures have passed laws—including state constitutional amendments—that prohibit same-sex marriage, while the District of Columbia and nine states—three of them last month—have legalized it.

But even where same-sex marriage is legal, married gay couples are denied a range of federal benefits under DOMA, which was passed in 1996.

In October, a Pew Research survey found that 49 percent of Americans support marriage equality, while 40 percent oppose it.

In May, President Barack Obama became the first sitting American president to support the right of same-sex couples to get marry.

Yet even where it is legal, married same-sex couples do not qualify for a host of federal benefits because the 1996 Defense of Marriage Act, or DOMA, passed by Congress, recognizes only marriages between a man and a woman.