The US Department of Justice took an important step in combating the epidemic of Republican vote suppression efforts on Friday. The Justice Department blocked a South Carolina law requiring voters to present photo identification, because the law would disproportionately disenfranchise minority voters. South Carolina is one of the states that under the Voting Rights Act (VRA), due to a history of discriminatory practices, must obtain pre-clearance from the Justice Department for new voting requirements. The Justice Department must certify that such laws are not discriminatory in their impact, not just in their intent.

According to South Carolina, 240,000 registered voters lack the requisite identification. That alone should be a cause for concern. But the legal problem for South Carolina arises from the fact that those without photo identification are more likely to be African-American than white. (They also tend to be younger, poorer and thus more Democratic-leaning.)

Voting rights experts say the Justice Department did the right thing. Unfortunately, in states that aren’t subject to pre-clearance, it doesn’t have the same power to protect voting rights. “The Department of Justice came to the only conclusion it could have—that South Carolina’s ID law, like others passed around the country, may disenfranchise tens of thousands of voters and is racially discriminatory in its impact,” says Tova Andrea Wang, an election reform expert at Demos. “The decision is legally correct,” says Daniel Tokaji, an election law professor at Ohio State University. “If the effect is to make it more difficult for minorities to vote than was the case before, then the law presumptively violates the VRA. Given that blacks are more likely to lack the required ID, it was hard for South Carolina seriously to argue that the law complies with the VRA.”

Wisconsin and Indiana, which unlike South Carolina are swing states, have similar new laws on the books. They aren’t subject to pre-clearance, meaning the Justice Department cannot stop them on the front end. After the fact, it can challenge them in court, but under a more stringent legal standard than applies in South Carolina. There are also other potential legal objections besides racial discrimination. The ACLU filed suit on December 13 against Wisconsin over its new requirement that voters show photo identification, saying it amounts to a poll tax. And that’s not the only possible legal battle likely to come: South Carolina may challenge the Justice Department’s decision, ultimately requiring the Supreme Court to weigh in.

However, this is a positive sign that the Justice Department’s civil rights division is taking voting rights seriously. States like Wisconsin and Indiana should be on notice that Justice will rigorously monitor enforcement for signs of disparate racial impact. “If the voter ID laws are implemented in a discriminatory fashion—for example, if predominantly people of color or people who are not English-proficient are being required to present ID when they come to vote—the DOJ can go after those places where it happens,” explains Wang.