The ruling is a blow to Democrats in the state who say the law could disenfranchise thousands of voters, especially in minority communities that rely upon neighbors and activists to collect and hand-deliver the ballots.
Friday, a 6-5 ruling by the 9th US Circuit Court of Appeals granted a preliminary injunction of the law; the Supreme Court's order stays that decision. There were no noted dissents.
In Arizona, voters can request an early ballot to be sent to them before the election. The voters can then mail it back or drop it off at a polling locations as long as it is received by 7 p.m. on Election Night.
Democrats in the state argued that thousands -- particularly those in towns near the border and in Native American reservations without reliable mail service -- have relied upon having their ballot collected by organizers in past years to ensure the ballots are received on time.
The law makes it a felony, punishable by a year in jail and $150,000 to knowingly collect "voted or unvoted early ballots" from another person. It provides for an exception for family members or caregivers.
"It is no secret that ballot collection and delivery has been particularly beneficial for Arizona's minority voters, and legislators who have not traditionally enjoyed broad support in those communities have repeatedly tried to restrict it," Democratic lawyer Marc Elias argued in his filing with the Supreme Court Saturday morning.
Arizona Secretary of State Michele Reagan praised the decision.
"We are extremely pleased the Supreme Court reversed the ninth circuit's decision, Reagan said in a statement. "This commonsense law simply ensures ballot security in the state of Arizona and we're relived that there will be no changes to the law this late in the election cycle. "
In briefs filed by lawyers for the Arizona, lawyers had argued that the law "will not actually have a discriminatory impact or anything more than a minimal burden on the right to vote," and lambasted the appeals court for blocking the "sensible" law so close to the election.
Joshua A. Douglas, an election law expert at the University of Kentucky College of Law, believed a major concern for justices could be the timing.
"This could be a close vote," Douglas said Friday. "I could see several justices worrying about the impact of the law while others will be more concerned with the timing issues."
The majority of the appeals court said it recognized that it was blocking the law close to the election but said that its injunction would not affect the state's "election processes or machinery."
"The only effect is on the third party ballot collectors, whose efforts to collect legitimate ballots will not be criminalized, pending our review," the majority said.
In a brief filed by the Arizona Republican Party and joined by the state attorney general, lawyers called the law a "well-reasoned" safeguard to a "fair and transparent election."
They argued that the challengers "have not and cannot meet their burden to overcome the important regulatory interests protecting voters and ensuring an orderly and fair election process."
They said the law was in effect for the primary election and that the challengers could not identify "a single voter whose ability to vote was burdened by the law."