A federal judge on Wednesday ruled Kentucky must recognize same-sex marriages legally performed in other jurisdictions.

Judge John G. Heyburn II of the U.S. District Court for the Western District of Kentucky said the Bluegrass State’s constitutional amendment that defines marriage as between a man and a woman is also unconstitutional.

“The court concluded that Kentucky’s denial of recognition for valid same-sex marriages violates the U.S. Constitution’s guarantee of equal protection under the law, even under the most deferential standard of review,” wrote Heyburn in his 23-page ruling. “Accordingly, Kentucky’s statutes and constitutional amendment that mandate this denial are unconstitutional.”

Four gay and lesbian couples who legally married outside Kentucky filed the lawsuit seeking marriage rights in their state.

Greg Bourke and Michael Deleon, a Louisville couple who has been together for 31 years and are raising two teenaged children, exchanged vows in Canada in 2004. Jimmy Meade and Luther Barlowe of Bardstown, who have been together for 44 years, tied the knot in Iowa in 2009.

Randell Johnson and Paul Campion of Louisville, who have been together for 22 years and have four children, married in California in 2008. Kimberly Franklin and Tamera Boyd exchanged vows in Connecticut in 2010.

Kentucky voters in 2004 overwhelmingly approved a constitutional amendment that defined marriage as between a man and a woman.

“Usually, as here, the tradition behind the challenged law began at a time when most people did not fully appreciate, much less articulate, the individual rights in question,” said Heyburn, who frequently refers to the landmark 1967 U.S. Supreme Court ruling that struck down Virginia’s interracial marriage ban in his decision. “For years, many states had a tradition of segregation and even articulated reasons why it created a better, more stable society. Similarly, many states deprived women of their equal rights under the law, believing this to properly preserve our traditions.”

Heyburn, who then-President George H.W. Bush appointed to the federal bench in 1992, also cited last June’s U.S. Supreme Court ruling that found a portion of the Defense of Marriage Act unconstitutional.

“The body of constitutional jurisprudence that serves as its foundation has evolved gradually over the past 47 years,” wrote Heyburn.

Eighteen states and D.C. have extended marriage rights to same-sex couples.

A federal judge last month ruled Oklahoma’s gay nuptials ban is unconstitutional. The U.S. Supreme Court less than two weeks earlier blocked any future same-sex marriages from taking place in Utah pending the outcome of an appeal of U.S. District Court Judge Robert Shelby’s December ruling that struck down the Beehive State’s gay nuptials ban.

A federal judge in Norfolk, Va., is expected to issue her ruling shortly in a lawsuit that challenges Virginia’s same-sex marriage ban.

“Today a Republican-appointed federal judge in Kentucky held – as did judges in Utah and Oklahoma weeks ago and as did the U.S. Supreme Court last year – that there is simply not legitimate justification for denying equal protection to same-sex couples, echoing the majority of Americans who support the freedom to marry, including a growing number of conservatives,” said Freedom to Marry President Evan Wolfson.

The Family Foundation of Kentucky, which filed an amicus brief in support of the commonwealth’s same-sex marriage ban, criticized Heyburn’s decision.

“Legislating same-sex marriage from the bench is not the will of the people,” said the group on its Twitter page.

Heyburn issued his ruling on the same day a federal judge in San Antonio heard oral arguments in a case that challenges Texas’s marriage amendment.

The American Civil Liberties Union and the ACLU of Missouri on Wednesday filed a lawsuit in state court on behalf of eight same-sex couples who are seeking recognition of their marriages legally performed in other jurisdictions. The Forum for Equality Louisiana on the same day filed an identical lawsuit in a federal court in New Orleans on behalf of four gay and lesbian couples who legally married outside the Pelican State.

Attorney General Eric Holder on Monday announced the Justice Department will now recognize same-sex marriages in civil and criminal cases and extend full benefits to gay spouses of police officers and other public safety personnel killed while on duty. This new policy applies to the 32 states that currently do not recognize same-sex marriages.