The Hawaii Campaign Spending Commission launched an investigation Thursday into the Pacific Resource Partnership’s involvement in the 2012 Honolulu mayoral race.

PRP, an advocacy group for union carpenters and contractors, spent $3.6 million during that election cycle, almost entirely on an effort to derail former Hawaii Gov. Ben Cayetano’s bid for mayor.

Cayetano had vowed to stop the city’s $5.26 billion rail project if elected, and PRP was a major advocate of the project.

Copies of some of the PRP emails obtained by Civil Beat after former Gov. Ben Cayetano filed suit.

PF Bentley/Civil Beat

Internal emails obtained as part of Cayetano’s defamation lawsuit against PRP have raised questions from the Campaign Spending Commission about whether the group properly reported all of its expenditures, particularly those related to hired political consultants.

Civil Beat recently reported that several of the consultants involved in PRP’s takedown of Cayetano were not listed in the spending reports of the group’s political action committee.

Those consultants include Texas-based opposition researcher Jason Stanford, local PR experts Jim McCoy and Barbara Tanabe, and Andy Winer, who at the time was working on Mazie Hirono’s U.S. Senate campaign.

PRP’s internal emails show all four had been working with the group many months before it officially launched its super PAC, yet there’s no clear indication in campaign spending records that any of them were paid by PRP.

Winer is a well-known political operative in Hawaii, and is currently the chief of staff for U.S. Sen. Brian Schatz.

Hawaii Campaign Spending Commission attorney Gary Kam said Thursday that his agency will focus on the “potential vendors” PRP used to carry out its campaign against Cayetano.

Kam said PRP could be fined if the Campaign Spending Commission’s investigation finds the group did not file complete reports with his agency.

PRP’s campaign against Cayetano was also one of the most sophisticated political operations ever seen on the islands.

The group attacked Cayetano’s record on the airwaves as well as in print, often using messages that were intended to paint him as corrupt.

PRP even sent canvassers door-to-door to sway voters against the former two-term Democratic governor, arming them with negative campaign literature as well as smart phones to track their progress.