Houston's Mayor Annise Parker has backed down in a row over whether to subpoena copies of sermons preached by the city's pastors.

Controversy broke out when the city's legal department launched proceedings to force ministers to hand over copies of documents, including sermons, that they had produced regarding the Houston Equal Rights Ordinance (HERO), otherwise known as the Bathroom Bill. HERO forbids discrimination in a wide range of categories including transgendered and intersex people. Opponents say that one consequence, that men would be allowed to use women's lavatories, is unacceptable; the subpoena was in response to a legal challenge by conservative pastors based on the city's refusal to accept petitions against the legislation.

Now the word 'sermons' has been removed from a new version of the subpoena. However, Parker's concession is unlikely to satisfy opponents who see the whole process as an assault on religious liberty, and it could still lead to sermons having to be produced.

Parker argued that the city's legal team needed material relating to how the petitions were generated. "We don't need to intrude on matters of faith to have equal rights in Houston and it was never the intention of the city of Houston to intrude on any matters of faith or to get between a pastor and their parishioners," she said.

"We don't want their sermons, we want the instructions on the petition process. That's always what we wanted and, again, they knew that's what we wanted because that's the subject of the lawsuit."

She said that opponents took advantage of the broad original language to misinterpret the city's intent.

In another twist to the story, former Arkansas governor Rev Mike Huckabee, a Southern Baptist minister, has intervened in the row. He has urged the nation's ministers of religion to send Bibles and copies of their sermons to Mayor Parker. He said on his Fox News show: "It ought to make you mad that the mayor thinks she can turn in her pastors. And so I got an idea. If she wants a sermon, here is my suggestion. I would like to ask every pastor in America, not only the ones in Houston, to send her your sermons and go ahead. Obviously she could use a few. And everybody watching the show ought to send her a Bible."

The former presidential candidate said: ""I hope she gets thousands and thousands of sermons and Bibles."

Houston has suspended the implementation of HERO until the case is resolved.