Texas is throwing down the gauntlet challenging the US Supreme Court's decision legalising gay marriage across the land.

The state's top lawman, the Texas attorney general, had advised clerks and justices of the peace that they're welcome to flout the law and refuse to marry same-sex couples if it conflicts with their religious beliefs, reports the Houston Chronicle.

State Attorney General Ken Paxton warned that they might face a fine or litigation — but promised support for defiant government officials.

"Numerous lawyers stand ready to assist clerks defending their religious beliefs, in many cases on a pro-bono basis, and I will do everything I can from this office to be a public voice for those standing in defence of their rights," vowed Paxton.

But he also pointed that such stands should not hold up gay marriages — that others could provide a marriage licence.

Paxton said his office has determined that state religious freedom laws would allow clerks to refuse to issue marriage licenses if there was someone else present — such as a deputy — who would be willing to help the couple.

The argument is based on the "undue burden" concept which maintains that civil servants can refuse to follow the law as long as there are other who can provide the service. It's the same concept that underlies abortion restrictions in the state.

In response to Paxton, Democratic state Senator Rodney Ellis is calling on the US Department of Justice to step in to protect gays' right to marry. He sent a letter to US Attorney General Loretta Lynch asking the department "monitor" the state and "intervene, if necessary, to ensure that Texas officials do not flout the Supreme Court's ruling and blatantly discriminate against same sex couples."

Despite Paxton's comments, many clerks in Texas, such as Travis County Clerk Dana DeBeauvoir, immediately began issuing marriages licences to same sex couples.

"We are public servants in a secular role to uphold the law of the land," DeBeauvoir told the Chronicle. "We have separation of church and state. We need to remember that."