AUSTIN, Texas (Reuters) - The Texas Senate on Tuesday preliminarily approved a Republican-backed bill that would restrict access to public bathrooms by transgender people over criticism from Democrats who said it was unnecessary, discriminatory and economically destructive.

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In a 21-10 vote almost along party lines, the Republican-dominated Senate gave preliminary approval to the Texas Privacy Act.

The bill would require people to use restrooms that correspond with the gender on their birth certificate, not the gender with which they identify.

Its backers said it is a common-sense approach to provide safety and keep sexual predators out of bathrooms.

After final approval, seen as a formality and expected on Wednesday, the bill goes to the Republican-controlled House, where analysts say its chances of passage are slim due to concern about the legislation’s potential economic impact.

Allowing transgender people to use public bathrooms corresponding to their gender identity rather than their birth gender has become the latest flashpoint in the long U.S. battle over lesbian, gay, bisexual and transgender (LGBT) rights.

“It is about a privacy issue for us women, for boys, for girls,” the bill’s sponsor, Republican Senator Lois Kolkhorst, told the body.

Democratic Senator John Whitmire said the bill was fatally flawed and would force transgender people like a bald transgender man with a beard to use a woman’s bathroom. He added that there are some 30 statutes in Texas law that punish sexual predators.

“We don’t need your bill to prosecute them,” he said in Senate debate.

The bill is similar to one enacted last year in North Carolina. That law prompted economic boycotts and the loss of sporting events that were estimated to have cost the state hundreds of millions of dollars.

In January, the Texas Association of Business released a study which said that if the legislation were enacted, it could cost Texas as much as $8.5 billion in the state’s gross domestic product and the loss of more than 185,000 jobs in the first year alone.

Republican Lieutenant Governor Dan Patrick, a Tea Party Christian who is a prominent backer of the Texas bill, has challenged the survey.

Nearly 70 businesses, including some of the state’s biggest employers such as American Airlines Group Inc, sent a letter to Republican leaders this month asking them to reject the bill on the grounds that it would “legalize discrimination.”