A federal appeals court ruled Wednesday that Texas's controversial voter ID law is discriminatory and violates Section 2 of the Voting Rights Act.

ThinkProgress describes it as "a stunning, unexpected decision from one of the most conservative federal appeals courts in the country," the New Orleans-based 5th U.S. Circuit Court of Appeals.

Signed into law in 2011, Senate Bill 14 has been called the strictest voter ID law in the nation. As the Texas Tribune explains: "Texas is among nine states categorized as requiring 'strict photo ID,' and its list of acceptable forms is the shortest."

The Tribune further reports:

Texas argued that opponents of the law had "failed to identify a single individual who faces a substantial obstacle to voting because of SB 14." In Wednesday's ruling, the majority rejected that argument. "For one thing, the district court found that multiple Plaintiffs were turned away when they attempted to vote, and some of those Plaintiffs were not offered provisional ballots to attempt to resolve the issue," the ruling stated. The majority also affirmed the lower court's finding that Texas' "lackluster educational efforts resulted in additional burdens on Texas voters."

The opinion states (pdf): "As the State would have it, so long as the State can articulate a legitimate justification for its election law and some voters are able to meet the requirements, there is no Section 2 violation. This argument effectively nullifies the protections of the Voting Rights Act by giving states a free pass to enact needlessly burdensome laws with impermissible racially discriminatory impacts. The Voting Rights Act was enacted to prevent just such invidious, subtle forms of discrimination."

The appeals court "also sent the case back to a district court to examine claims by the plaintiffs that the law had a discriminatory purpose," as Reuters reports, and to fix the "discriminatory effect" of the 2011 law—in time for the November elections.

Myrna Pérez, deputy director of the Brennan Center's Democracy Program, called the ruling "an enormous victory for voters in Texas."

"The votes of more than 600,000 Texans were at stake in today's ruling," she said. "The court sent a message that discriminatory photo ID laws are an affront to our democracy."

Yet the fight isn't over, said Representative Trey Martinez Fischer, chairman of the Mexican American Legislative Caucus of the Texas House of Representatives, noting the erosion of voting protections over the past three years. He warned that "we cannot rely on the courts to protect our voting rights. Certain states, including Texas, have demonstrated that they will not relent in their fight against unfettered access to the ballot box for all Americans."

"Whatever procedural course this case follows," he continued, "Congress must act to restore the Voting Rights Act to put an end to the increasingly subtle and sinister efforts to disenfranchise those who challenge the status quo."

Indeed, said Wade Henderson, president and CEO of the Leadership Conference on Civil and Human Rights, referring to the "arduous litigation" brought about by the gutting of the Voting Rights Act in Shelby County v Holder: "The scope of this problem is massive. Shelby ushered in a resurgence of voter discrimination and now politicians across the country have been choosing their voters instead of having voters choose them."

The law had already faced numerous legal challenges. As NBC News previously reported, "A federal judge declared the law unconstitutional and found that more than 600,000 registered Texas voters did not have the kinds of IDs required by the new law."

"But an appeals court issued a stay, saying it wanted to review the law further, and blocked that ruling, allowing the law to go into effect," the NBC report continued. "Challengers then asked the U.S. Supreme Court to lift the stay, which would have put the legal hold back into place."

Then, the Supreme Court in April let the law remain in effect, but said, "If, on or before July 20, 2016, the Court of Appeals has neither issued an opinion on the merits of the case nor issued an order vacating or modifying the current stay order, an aggrieved party may seek interim relief from this Court by filing an appropriate application."

The new ruling "sets up a potential Supreme Court showdown over the contentious issue of state photo ID rules," USA Today reports.