The U.S. Supreme Court on Thursday left in place a lower-court ruling that relaxes voting restrictions in Rhode Island during the coronavirus pandemic.
The justices rejected an emergency request made by the Republican National Committee and the state's Republican Party.
The decision means that mail-in ballots will not, as usual, have to be accompanied by the signatures of two witnesses or one notary.
The unsigned order left intact a decision by Rhode Island-based U.S. District Court Judge Mary McElroy, who ruled on July 30 that the Republican groups had waited too late to intervene in the case. The order said three of the nine justices, conservatives Clarence Thomas, Samuel Alito and Neil Gorsuch, would have granted the request.
The Republicans wanted to challenge a consent decree suspending the signature requirement that McElroy had approved.
The case was originally brought against the state by voting rights groups, including Common Cause Rhode Island.
On August 7, the Boston-based 1st U.S. Circuit Court of Appeals declined to put McElroy's ruling on hold.
The Supreme Court on July 2 had granted a similar request made by Republican officials in Alabama.
Thursday's order noted that, unlike the Alabama case, state officials in Rhode Island supported the settlement.
Republican President Donald Trump, who is up for re-election on November 3, has frequently attacked the possibility of mail-in ballots being used widely as the nation reels from the pandemic that has so far killed more than 160,000 Americans.
Trump has made unsubstantiated claims that mail-in ballots are especially vulnerable to fraud and suggested that their widespread use would lead to a "rigged election."