New Jersey became the third US state to offer civil unions to same-sex couples when a new law went into effect on Monday. Couples who have civil unions or marriages from other states or countries were automatically considered in a civil union in New Jersey, and they can affirm their vows as of Monday. That accounts for about a few hundred of the state's estimated 20,000 gay couples. New Jersey's state Supreme Court ruled in October that the state must extend all the rights of marriage to gay couples and left it to lawmakers to decide whether to provide those rights in the form of marriages, civil unions or something else. Lawmakers opted for "civil unions," in part because of opposition from legislators who objected on religious grounds to calling it "marriage." Gay rights advocates say they will keep pressing for New Jersey to become the second state in the United States to allow gay marriage. Vermont and Connecticut have civil union laws, but Massachusetts is the only US state to allow same-sex marriages. Same-sex marriage is legal in Canada, Belgium, the Netherlands, Spain and South Africa.