Louisiana clerks of court should immediately issue marriage licenses to same-sex couples and could face both public and personal civil liability if they fail to do so after Friday's landmark U.S. Supreme Court ruling, according to an LGBT advocacy group.

In a letter written Sunday, Forum for Equality Louisiana put the Louisiana Clerks of Court Association on "formal notice," urging them to begin giving out marriage licenses to gay and lesbian couples, saying "even a short delay in the ability of same-sex couples to exercise their fundamental rights to marry or to have their marriages recognized constitutes irreparable injury" and that "every single state except Louisiana has begun following the Supreme Court's ruling."

The 25-day waiting period for Supreme Court rulings to become official, which the clerk's association cited as the reason they're holding off on issuing the licenses, is not actually required when the high court declares a constitutional right, wrote Christopher Otten, the organization's chair, who penned the letter.

Legal experts believe there is no chance the Supreme Court will rehear the case. The 25 days is the amount of time given to challenge the court's rulings.

Debbie Hudnall, the executive director of the state clerks association, was not immediately available for comment Monday morning.

On Friday, Hudnall said her agency's lawyers advised following the 25-day rule and the guidance of Louisiana Attorney General Buddy Caldwell. Caldwell, who didn't specifically refer to the 25-day lag, said in a statement his office "has found nothing in today’s decision that makes the Court’s order effective immediately.”

Forum for Equality, in its letter, quoted Justice Anthony Kennedy, who wrote in his opinion, "The Court now holds that same-sex couples may exercise that fundamental right to marry. No longer may this liberty be denied to them."

Almost all of the states that did not allow gay marriage before Friday -- including Southern states such as Texas, Tennessee, Arkansas, Georgia and Kentucky -- began issuing licenses after the Supreme Court's announcement. At least one such license was issued in Mississippi, which later held off on giving out more licenses, citing the state's case being tied up in the U.S. 5th Circuit Court of Appeals.

Only Louisiana did not issue any licenses to same-sex couples.