The Texas Supreme Court denied an effort by Republicans to throw out more than 120,000 votes that had already been cast at drive-through locations in Harris County, leaving Republicans’ only remaining option at the federal level.
The ruling from the court came without comment.
The effort to get rid of the votes from Harris County, which includes Houston and is largely Democratic, now hinges on a nearly identical effort at the federal level, where a judge has called an election-eve hearing for Monday.
The lawsuit contends that the 10 drive-through voting sites in Houston, the nation’s fourth-largest city, are operating illegally and are arranged in locations that favor Democrats.
The system was put in place for the first time this year by Chris Hollins, the Harris County clerk, with unanimous approval by county commissioners, after being tested in a pilot program over the summer.
More than 127,000 voters have cast ballots at the sites, and the number could grow to more than 135,000 through Election Day on Tuesday, said Susan Hays, a lawyer for Harris County. She said county officials planned to vigorously challenge the suit, which she described as an act of “voter suppression.”
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“It’s nuts,” she said. “Votes should count.”
Democrats were hopeful on Sunday that the decision from the all-Republican Texas Supreme Court would bode well for their battle at the federal level.
The case will be heard on Monday morning by Judge Andrew S. Hanen of the United States District Court for the Southern District of Texas, who was appointed by President George W. Bush.
In a motion on Friday asking to intervene in the case, Democrats said it threatened to “throw Texas’ election into chaos by invalidating the votes of more than 100,000 eligible Texas voters who cast their ballots” at the drive-through sites. The motion was filed by the Democratic Senatorial Campaign Committee, the Democratic Congressional Campaign Committee and the campaign of M.J. Hegar, a Democratic candidate for the Senate in Texas.
The plaintiffs, who include State Representative Steve Toth and the conservative activist Steve Hotze, argue that drive-through voting “is a violation of state and federal law and must be stopped.”
In a telephone interview on Saturday, Mr. Toth said that only the Legislature had the authority to put in place a drive-though voting system. He also said the arrangement of the sites was tilted toward Democratic voters, noting that Mr. Hollins is vice chairman of finance for the Texas Democratic Party.
“If Hollins is really concerned that everybody is accurately represented, why is it that nine of the 10 are set up in predominantly Democratic areas?” said Mr. Toth, who represents part of neighboring Montgomery County.
He denied that the lawsuit was aimed at blunting Democratic momentum amid record rates of early voting in Houston and other strongly Democratic areas in the last days before the election.
“We’re not the ones who are disenfranchising anybody,” he said. “This is Hollins who did this.”
In a statement on Twitter on Saturday, Mr. Hollins said drive-through voting was “a safe, secure and convenient way to vote,” adding: “Texas Election Code allows it, the Secretary of State approved it, and 127,000 voters from all walks of life have used it.”
He said that his office was “committed to counting every vote cast by registered voters in this election,” and that voters would be notified if court proceedings required them to take any additional steps.