There are some clear differences or distinctions between the Texas act (SB14) and the Indiana law upheld by the SCOTUS. In particular, under the Texas law one can not get a free id without a birth certificate. Justice Stevens approved the Indiana law in part because one could provide alternative documents to get the free id . http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=US&vol=000&invol=07-21&friend=nytimes In footnote 18 of Justice Stevens opinion, the fact that the Indiana statute did not require birth certificates was important to the court
Footnote 18
As petitioners note, Brief for Petitioners in No. 07-21, p. 17, n. 7, and the State's "Frequently Asked Questions" Web page states, it appears that elderly persons who can attest that they were never issued a birth certificate may present other forms of identification as their primary document to the Indiana BMV, including Medicaid/Medicare cards and Social Security benefits statements. http://www.in.gov/faqs.htm; see also Ind. Admin. Code, tit. 140, §7-4-3 ("The commissioner or the commissioner's designee may accept reasonable alternate documents to satisfy the requirements of this rule"
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There is a good state court case from the Missouri Supreme Court that held that any law that requires one to pay for a birth certificate in order to vote is a poll tax.
http://www.advancementproject.org/news/newsletters/democracy-in-action-volume-october-2006/the-missouri-supreme-court-declares-missour
I am hoping that the Department of Justice will be arguing that the Texas act is indeed a poll tax in the trial that is taking place in DC. I think that the facts and law support this position.