The dispute involves electronic voting machines.
A three-judge panel granted an injunction, sought by the state Democratic Party, that bars Dallas County from using the machines until Justice Department clearance is given.
The 2008 lawsuit was filed after a recount favored Republican incumbent Linda Harper-Brown over Democrat Bob Romano in a Texas House race.
The Texas secretary of state's office is also studying the ruling.
County attorney Leon Carter declined immediate comment.
Texas Democratic Party Chairman Boyd Richie called the ruling, made public Monday, a "victory for Texas voters and their right to cast a vote that counts."