“When private citizens form ‘ballot security forces’ and attempt to take over the State’s legitimate role of overseeing and policing elections, the risk of voter intimidation — and violating federal law — is significant,” the department said in a “statement of interest” filed in the case.

The League of Women Voters alleged that several organizations planned “widespread campaigns to surveil and intimidate Arizona voters at ballot drop boxes and baselessly accuse them” of voter fraud.

The drop boxes, intended to provide a secure, convenient place to submit ballots, have become a symbol of mistrust in elections among many supporters of former president Donald Trump.

Trump and his allies nationally and in Arizona have urged supporters to monitor outdoor drop boxes, an outgrowth of the discredited film “2000 Mules” that claims drop boxes were stuffed with fraudulent ballots during the 2020 election.

News of the Justice Department filing with its strong language about voter intimidation was welcomed by voting rights advocates, and Arizona officials who have been increasingly alarmed by outside groups congregating around drop boxes and recording videos of voters and their vehicles.

“To have folks standing outside of drop boxes, armed in tactical gear, with body armor, that is unprecedented,” said Bill Gates, the chair of the Republican-led Maricopa County Board of Supervisors. The filing, Gates said, showed “that there is a limit — there’s a balance between the First Amendment rights that people have and also the right that people have to not feel intimidated when voting. That point was made very strongly.”

The Arizona lawsuit is one of many claims from battleground states that voters are being intimidated when they place ballots in drop boxes. Arizona Secretary of State Katie Hobbs (D) referred a report of voter harassment at drop boxes to the Justice Department on Oct. 20. Attorney General Merrick Garland last week stated that the department “will not permit voters to be intimidated” during the midterm elections.

But Monday’s filing marks the first time this election cycle that the department has entered an ongoing case involving drop boxes in this way. The department specifically made reference to photographing voters at drop box sites, sometimes by armed vigilantes.

“Video recording or photographing voters during the voting process has long been recognized to raise particularly acute concerns,” the department’s Monday filing said.

The filing comes after a federal district court judge in Arizona, Michael Liburdi, on Friday refused in a related case to block groups from monitoring drop boxes. He said in a case brought by the Arizona Alliance for Retired Americans that there was insufficient evidence to warrant court intervention of an activity protected by the First Amendment.

The department in its filing did not offer a specific prescription in the case but argued that it is possible to craft an injunction blocking threatening activity consistent with the First Amendment’s protection of free speech and assembly.

“While the First Amendment protects expressive conduct and peaceable assembly generally, it affords no protection for threats of harm directed at voters,” the department’s lawyers wrote.

Voting rights advocates applauded the department’s action.

“The filing acknowledges the serious threat that voter intimidation, like we are seeing in Arizona, has to our democracy,” said Jessica Marsden, counsel to Protect Democracy, which filed the lawsuit on behalf of the League of Women Voters.

Danielle Lang, senior director for voting rights at the Campaign Legal Center, said the statement of interest was a strongly worded, significant addition to the case.

“It’s notable that this compelling brief was filed in such a short time frame,” following Liburdi’s decision not to intervene, Lang said.

The League of Women Voters is asking for a court order to ban armed vigilantes from gathering near the drop boxes and a hearing on that request is scheduled for Tuesday.

The hearing comes as one of the defendants in the league’s lawsuit, the Lions of Liberty, has been dropped from the case after agreeing to halt its drop box monitoring program. Luke Cilano, a board member with the Lions of Liberty in Yavapai County, questioned the department’s decision to get involved.

“Why would they be making statements on anything that is a states’ rights issue unless they’re trying to subvert the right of the state?” he said Monday.

Officials in Maricopa County, home to metro Phoenix and the largest voting population in the swing state, have urged voters to contact law enforcement or the secretary of state’s office if they feel uncomfortable while pulling up to the drop boxes to deposit ballots.

The secretary of state’s office reviews the complaints and determines whether they should be referred to the Justice Department and the state attorney general’s office.

State elections officials say they have received more than a dozen complaints about intimidation at drop boxes since early voting began Oct. 12. Through an open records request, The Washington Post received copies of complaints referred to law enforcement.

“I dropped off my ballot at the Maricopa County Recorders office and there were two men filming everyone as they drove through,” one voter wrote in a submission about their experience while voting in downtown Phoenix on Wednesday afternoon. “While this may not be illegal to do, it is very uncomfortable and feels intimidating.”

Wingett Sanchez reported from Phoenix.