AUSTIN, Texas (Reuters) - The Republican-controlled Texas Senate gave preliminary approval on Tuesday to a bill that restricts bathroom access for transgender people, endorsing a piece of legislation denounced by civil liberties advocates as discriminatory.

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Final Senate adoption of the bill was possible later on Tuesday or Wednesday. The measure would then be sent to the state House of Representatives, where passage during a 30-day special legislative session that ends in mid-August is less certain despite a Republican majority in that body as well.

The preliminary vote in the Senate was 21-10, with one Democrat crossing the aisle to vote with the Republican majority in favor of the measure, Senate Bill 3.

Enactment in Texas, the most-populous Republican-dominated state, could give momentum in other socially conservative states for additional action on an issue that has become a flashpoint in the U.S. culture wars.

The Texas measure requires that all restrooms, showers and locker rooms in public schools and other state and local government facilities “must be designated for and used only by persons of the same sex as stated on a person’s birth certificate,” as opposed to their gender identity.

The measure also would overturn local ordinances affirming transgender bathroom rights in such cities as Austin, San Antonio and Dallas.

Supporters, including Republican Lieutenant Governor Dan Patrick, a staunch social conservative, have said the proposed bathroom restrictions promote public safety and protect vulnerable women and children.

Momentum for so-called bathroom bills stalled earlier this year when a similar law in North Carolina was partially repealed in March. The original law prompted boycotts by a number of athletic organizations and businesses that were estimated to have cost the state hundreds of millions of dollars.

Opponents in Texas warned of a similar backlash.

“The state of Texas cannot afford discriminatory acts,” Democratic Senator Borris Miles said during debate on the bill.

The bill’s sponsor, Republican Senator Lois Kolkhorst, said there was no solid evidence showing that enacting the bill would hurt the state’s economy.

“Perhaps we will find that this one bill will lead to more economic activity,” she said.

Business leaders, socially progressive clergy and police chiefs of several major Texas cities have called on lawmakers to halt the bathroom bill, saying it does not protect the public.

Civil rights groups said there were already laws on the books protecting people from sexual assaults and voyeurism, and that enactment of SB 3 would further endanger transgender people, who are more prone to be victims of violence.

The Texas Senate previously passed a bathroom bill during the regular legislative session that ended in May, but the measure died in the House, under pressure from pro-business Republicans.

Texas House Speaker Joe Straus, a moderate Republican who steers that chamber’s agenda, has said such measures are unnecessary and raise worries of economic harm.