Two years after Texas became one of the last states to allow transgendered people to use proof of their sex change to get a marriage license, Republican lawmakers are trying to roll back the clock.

Advocates for the transgendered say a proposal to bar transgendered people from getting married smacks of discrimination and would put their legally granted marriages in danger of being nullified if challenged in court.

One of the Republican sponsors of the legislation said he's simply trying to clean up the 2009 law in a state that bans same-sex marriage under the constitution.

"The Texas Constitution," Sen. Tommy Williams said, "clearly defines marriage between one man and one woman."

The legislation by Williams, of Houston, and Rep. Lois Kolkhorst, of Brenham, would prohibit county and district clerks from using a court order recognizing a sex change as documentation to get married, effectively requiring the state to recognize a 1999 state appeals court decision that said in cases of marriage, gender is assigned at birth and sticks with a person throughout their life even if they have a sex change.

Most states allow transgendered people to get married using a court order that also allows them to change their driver's license, experts said. Some advocates for the transgendered say the Texas proposal would not only prevent future transgendered marriages but also open up the possibility that any current marriage could be nullified.