Mexico's Supreme Court is expected to rule on a gay marriage law, possibly as early as this week.

Mexico City lawmakers legalized gay marriage in December and the law went into effect in March. It gives gay and lesbian couples all the rights and responsibilities of marriage, including the right to adopt children. Previously, the city government recognized gay couples with civil unions, but gay adoption was banned.

Saying it was duty-bound to protect children, the federal Attorney General's Office has challenged the law. The federal government claims the law is unconstitutional because it “strays from the responsibility of the government to place a priority on safeguarding the interests of children.”

The federal government is controlled by the conservative PAN Party. Mexico City lawmakers approved the law over the objections of local PAN leaders and the Roman Catholic Church.

Mexico's Roman Catholic archbishop, Cardinal Noberto Rivera Carrera, called the law “immoral” and “reprehensible.”

Nearly 10% of Mexicans call Mexico City home, making it the country's most populous city.

City officials have claimed that the federal government's actions are politically motivated. For instance, no Mexican state has defined marriage as a heterosexual union in its constitution. And unlike the United States, there is no federal law banning gay marriage. Social conservatives fear gay marriage spreading out from Mexico City as state courts recognize the marriages of gay and lesbian couples.

The city has expressed confidence the high court will rule in its favor.

Several Latin American countries have followed Mexico City's lead. Argentina approved a gay marriage law last month. Chile, the last country on the continent to allow divorce, Uruguay, and Paraguay say they'll consider a gay marriage law. Peru will debate a bill that recognizes gay and lesbian couples with civil unions.