TALLAHASSEE -- The U.S. Supreme Court on Tuesday gutted a key part of the landmark Voting Rights Act that for decades sought to protect voters, including those in five Florida counties, against racially discriminatory laws.

In a 5-4 decision, justices said Congress must devise a new formula to determine which states and counties should remain subject to federal oversight of election law changes. They said the current criteria, established between 1965 and 1975, do not reflect today’s racial progress.

“In 1965, the states could be divided into two groups: those with a recent history of voting tests and low voter registration and turnout, and those without those characteristics,” Chief Justice John Roberts wrote for the majority. “Congress based its coverage formula on that distinction. Today the nation is no longer divided along those lines, yet the Voting Rights Act continues to treat it as if it were.”

Roberts was joined by justices Antonin Scalia, Anthony M. Kennedy, Clarence Thomas and Samuel A. Alito Jr. Justice Ruth Bader Ginsburg dissented, joined by justices Stephen G. Breyer, Sonia Sotomayor and Elena Kagan.

The court did not address the concept of federal oversight, called preclearance, itself. Under that part of the 1965 law, voting changes must be approved by the federal government or federal courts before they take effect to protect minority voters.

However, without a formula to determine which states or counties should be subject to federal review, that part of the law cannot be enforced.

Nine states, mostly in the South, and parts of six others, including Florida, had been subject to the law. The affected Florida counties are Hillsborough, Monroe, Collier, Hardee and Hendry.

“Clearly, we won’t be needing to seek preclearance going forward,” said Hillsborough County Attorney Chip Fletcher.

Last summer, the federal preclearance process prompted a panel of three federal judges to strike down the Florida Legislature’s reduction of early voting days from 14 to eight. Democrats accused Republican lawmakers of voter suppression, and the judges essentially agreed, writing that shortening early voting days was “analogous to closing polling places in disproportionately African-American precincts.”

The judges later approved a plan under which the five counties agreed to offer eight days of early voting for 12 hours a day.

“This governor and this Legislature are walking advertisements as to why federal oversight is needed,” said Howard Simon, executive director of the American Civil Liberties Union of Florida.

Facing severe criticism because of long voting lines last fall, the Legislature changed the law again this spring, this time to expand early voting sites and give counties the option to offer up to 14 days of early voting for 12 hours a day, not eight hours as before.

But Tuesday’s ruling means those changes won’t be subject to federal oversight in the five counties unless Congress acts quickly. The Senate Judiciary Committee will hold a July hearing to begin the process of retooling the law.

President Barack Obama said he was “deeply disappointed” with the decision and said it “upsets decades of well-established practices that help make sure voting is fair, especially in places where voting discrimination has been historically prevalent.”