Massachusetts Attorney General Martha Coakley led a coalition of 14 states in filing a brief with the Ninth Circuit Court of Appeals urging the court to strike down gay marriage bans in Nevada and Hawaii.

“Our experience in Massachusetts clearly shows that allowing same-sex couples to marry has only strengthened the institution of marriage,” Coakley said. “We urge the Courts to strike down these unconstitutional bans which only serve to discriminate against gay and lesbian individuals and their families.”

Thirteen states in addition to Massachusetts joined in the brief, including California, Connecticut, Delaware, Iowa, Illinois, Maine, Maryland, New Hampshire, New Mexico, New York, Oregon, Vermont and Washington, as well as the District of Columbia. Neither Oregon nor Illinois allow gay couples to marry.

“[T]he states favor – and therefore encourage – marriage over transient relationships because marriage promotes stable family bonds, fosters economic interdependence and security for members of the marital household, and enhances the physical and emotional well-being of both the partners to the marriage and their children. … All of these interests are furthered by including same-sex couples from the institution.”

Nevada currently recognizes gay couples with domestic partnerships, while Hawaii allows civil unions. Neither union is recognized by the federal government, which does recognize the legal marriages of gay couples pursuant to a Supreme Court decision in June which struck down the Defense of Marriage Act (DOMA).

Hawaii on Monday opens a special session called by Governor Neil Abercrombie to consider a proposed bill which would make Hawaii the 15th state to legalize such unions.

(Related: In Hawaii ad, NOM says agree with gay marriage or you'll be punished.)