Government officials say the receptacles are illegal and could lead to voter fraud, but the party says it will continue the practice.
The California Republican Party has admitted responsibility for placing more than 50 deceptively labeled ''official'' drop boxes for mail-in ballots in Los Angeles, Fresno and Orange Counties -- an action that state officials said was illegal and could lead to voter fraud.
The dark gray metal boxes have been popping up over the past two weeks near churches, gun shops and Republican Party offices, mostly in conservative areas of a deep-blue state, affixed with a white paper label identifying them as either an ''Official Ballot Drop off Box'' or a ''Ballot Drop Box.''
To the average voter, they are virtually indistinguishable from drop-off sites sanctioned by the state, which are governed by strict regulations intended to prevent the partisan manipulation of ballots.
The actions of the largely marginalized state party come at a moment when Republicans and Democrats are engaged in a bitter national struggle over voting rights, with President Trump's allies accusing Democrats in Minnesota and elsewhere of undermining the integrity of the electoral process by expanding absentee voting and other measures to increase ballot access.
On Monday, California's secretary of state, Alex Padilla, and Attorney General Xavier Becerra sent a cease-and-desist order to the state- and county-level Republican parties, ordering them to remove the boxes. They also urged voters who might have unknowingly dropped off their ballots in the receptacles to sign up with the state's voter tracking website to ensure their vote is counted.
''Misleading voters is wrong regardless of who is doing it,'' Mr. Padilla said in a conference call with reporters, adding that the boxes ''are not permitted by state law.''
Mr. Becerra called the boxes ''fake,'' adding that it was ''illegal to tamper with a citizen's vote.'' He warned that anyone ''engaging in this activity'' could be subject to criminal prosecution or civil action.
Hector Barajas, a spokesman for the California Republican Party, said the party would continue to distribute the boxes, without adding any label identifying them explicitly as Republican ballot drops.
Mr. Barajas -- who disclosed that Republicans were responsible for the boxes only after being bombarded by questions by reporters on Monday -- said the party's actions were legal because state law did not restrict ''ballot harvesting,'' a practice that allows a third party to collect voters' completed ballots.
Mr. Trump and his supporters have decried the practice as corrupt when Democrats have been accused of collecting bundles of ballots, which is legal in 26 states but subject to verification requirements.
''There is nothing in any of the laws or regulations cited in that advisory that indicate private organization drop boxes are not permitted,'' said Mr. Barajas, who blamed Democrats for blocking anti-harvesting legislation.
''The way Democrats wrote the law, if we wanted to use a Santa bag, we could,'' he said. ''A locked heavy box seems a lot safer,'' Mr. Barajas said.
Mr. Padilla dismissed that claim, telling reporters that the boxes were not covered by legal protections, because they were intended to ''mislead voters and erode the public trust.''
State officials have not alleged that operatives from either party have engaged in the selective harvesting of ballots placed in the illegal boxes. The ballots will be counted if they are received, even if they do not have a third-party signature typically required for collected mail-in votes, Mr. Padilla said.
Republican officials purchased about 100 of the boxes in recent weeks in an attempt to boost turnout, especially in competitive down-ballot races, as party leaders fret about Mr. Trump's drag on other Republicans, an operative with direct knowledge of the effort said.
They had installed about half of them by the time Mr. Padilla and other state officials took notice over the weekend.
State officials quickly ordered an investigation into the boxes, and Mr. Padilla sent a memo to county elections officials urging them to investigate the unauthorized boxes in order to ''guarantee the security and chain of custody of vote-by-mail'' ballots placed in them.
In his memo, he reminded local officials that creating an illegal polling site was a felony punishable by up to four years in prison.
Mr. Padilla's office received a report on Saturday that a metal box with a misleading sign suggesting that it was an official site to drop off mail-in ballots had been placed in front of the Freedom's Way Baptist Church in Castaic, northwest of Los Angeles.
And last week, a supporter of a Republican congressional candidate in Orange County, Michelle Steel, posted a picture of himself on Twitter dropping off a ballot at one of the party's boxes.
In the post, Jordan Tygh, a regional field director for the California Republican Party, flashes a thumbs-up over the caption, ''Doing my part and voting early,'' according to The Orange County Register, which first reported on the use of the boxes.
The post has since been deleted.
PHOTO: State officials in California have ordered an investigation into more than 50 deceptively labeled ''official'' drop boxes. (PHOTOGRAPH BY Mike Blake/Reuters FOR THE NEW YORK TIMES)