Political action committees are spending more than $1 million on the Honolulu mayoral campaign in an effort to persuade voters to either support or reject Mayor Kirk Caldwell’s re-election bid.

The union-backed Workers for a Better Hawaii has reported paying $750,307.54 to three advertising and marketing companies in support of Caldwell, more than half of that total since Monday. Among the group’s backers is the Hawaii Regional Council of Carpenters, the union that backed Pacific Resource Partnership.

In 2012, the now-defunct pro-rail PRP Political Action Committee spent $3.6 million on advertising trying to persuade voters to reject former Gov. Ben Cayetano’s mayoral campaign. Cayetano subsequently filed a defamation lawsuit against the PAC, which was settled when PRP agreed to issue a public apology and donate $125,000 to two charities.

Two other groups have also invested in this year’s mayoral election:

>> The newly formed Save Our City LLC told the Honolulu Star-Advertiser that it is spending at least $300,000 to oppose Caldwell’s re-election and support his opponent, former U.S. Rep. Charles Djou.

>> A third PAC, headed by the United Public Workers, which represents most blue-collar government workers in Hawaii, has also begun running ads supporting Caldwell, although it has not provided information on how much it is spending and why.

Save Our City and Workers for a Better Hawaii are both “independent expenditure committees,” or “super PACs,” while the UPW PAC is not.

The U.S. Supreme Court’s 2010 Citizens United decision allows noncandidate committees to spend an unlimited amount of money to advocate for the election or defeat of “a clearly identified candidate” as long as there are no direct candidate contributions and there is no coordination between the organization and either any candidate or party. Typically, an individual or organization would not be allowed to donate more than $4,000 to a candidate in this year’s mayoral election.

Super PACs are different from traditional PACs like the UPW group in that they are also allowed to receive an unlimited amount of money from donors as long as there is no coordination between them and candidates. It also cannot contribute money to any individual’s campaign.

Workers for a Better Hawaii, which also ran ads in support of Caldwell four years ago, has spent $750,307 since Oct. 18, according to electioneering communication reports that are required to be filed — under a new statute that took effect this year — by any candidate and noncandidate organizations within 24 hours of each time it spends $2,000 or more.

THE first few reports list the Hawaii Government Employees Association, which represents most white-collar government workers in the state, and its affiliate union organizations AFSCME and the Hawaii State AFL-CIO as the top three contributors for the expenditures. The last three reports, however, list HGEA, the Hawaii State AFL-CIO and the Hawaii Regional Council of Carpenters.

Officers with Workers for a Better Hawaii, all of whom list an HGEA address, have not returned calls. A spokeswoman for HGEA said she is not authorized to speak for the PAC.

The ads speak of how Caldwell supports seniors and women’s causes.

Meanwhile, Save Our City LLC has been running ads calling on Oahu voters to elect Djou. The group was registered by Sarah Houghtailing, owner of TJ’s Sports Bar and Grill on Kapiolani Boulevard.

In an email response to questions, Houghtailing said the group includes “family and friends mostly along with one union.” The identities of the parties will be made known Monday in its campaign spending report, showing all money collected and disbursed, she said.

Save Our City had not filed any electioneering communications reports with the Campaign Spending Commission so it is unknown how much is being spent or who is paying for the ads. Houghtailing, in an email, said the organization intends to spend about $300,000.

SAVE Our City and its website, savehonolulu.org, are unrelated to the now defunct, anti-rail PAC SaveOurHonolulu.com, which was led by rail opponent and University of Hawaii law professor Randall Roth. Houghtailing emphasized her group is pro-rail.

“The main purpose of our group is to get someone in office that will complete the rail, hopefully not any more over budget than is currently expected,” she said.

The Save Our City ads blame Caldwell for mismanaging the city’s now $8 billion rail project, arguing that the mayor was too busy “moonlighting” and “enriching himself” as a member of the Territorial Savings Bank’s board of trustees. (Caldwell earns a base amount of about $50,000 from the bank and has received about $150,000 more in stock shares in recent years due to a one-time grant approved by stockholders in 2010. The Ethics Commission said Caldwell had no conflict by continuing in the Territorial position.)

Last week, the Campaign Spending Commission fined Save Our City $150 for violating state laws that say a PAC’s advertising needs to say clearly and prominently that it was done with or without the approval or authority of any candidate. The commission fined the super PAC $25 for each of six instances: four radio ads, the website savehonolulu.org and a flier it has distributed.

NEITHER Save Our City nor the UPW PAC had submitted electioneering communications reports as of Tuesday, despite running TV ads.

UPW and its PAC officials could not be reached Wednesday.

Kristin Izumi-Nitao, the Campaign Spending Commission’s executive director, said she is aware that Save Our City has run ads without submitting electioneering communications reports. Her staff is discussing the situation with the group, she said.