HELENA, Mont. (AP) — It was a tantalizing offer for candidates for state legislative offices, many of whom had never mounted a campaign before.

A national anti-union organization offered candidates in five states a "deadly effective" series of seven custom-written letters that would be signed with their digitally-scanned signatures and mailed to thousands of voters in the final weeks before Election Day. For that personal touch, female National Right to Work Committee field workers would rewrite by hand a "wife letter" — which staffers said was a particularly potent appeal to voters.

The organization offered the mail to candidates in Montana, Iowa, Kentucky, Indiana and Nevada during the 2010 elections, according to thousands of emails, letters, mailers and testimony obtained by The Associated Press through a public records request.

While the organization has not been accused of wrongdoing, the documents are being used in civil cases against nine of the 14 Montana candidates who received "the works" package. They are accused of illegally coordinating with and taking unreported contributions from Right to Work and its affiliates.

The group's spokesman, Patrick Semmens, did not respond to multiple requests for comment.

The documents, more than 14,000 in total, had been subpoenaed by Montana's elections regulator from the computers of Right to Work's field operatives, and provide a rare look into the inner workings of so-called "dark money" groups.

Typically registering as social welfare organizations, these groups can raise money and aren't required to reveal the names of their donors. Those groups are not allowed to have political advocacy as their primary purpose, and Right to Work has said in tax filings that it does not participate in political campaign activities.

Campaign finance advocates fear the wealthy are using the groups to influence candidates out of public view.

Montana, Iowa and Kentucky had bans against direct contributions from corporations such as Right to Work to candidates in 2010, according to the National Conference of State Legislatures. Indiana had a $2,000 corporate contribution limit to legislative candidates and Nevada's limit was $5,000.

Candidates are required to report all cash and in-kind contributions, but Right to Work either provided candidates its services for free or at cost, according to the documents. Candidates charged in Montana paid below market value for the mailings, the elections regulator alleged. Many candidates did not report their participation in the mail program or any additional candidate programs the group offered.

In Montana, that included connecting voters to fundraising resources, website design and what Montana Right to Work staffer Christian LeFer called "the best voter lists in the state," according to the documents. LeFer offered the full range of services to 14 Montana Republican candidates in 2010.

LeFer said in the documents that everything "for invitees" was done for free or at cost.

Montana began to investigate Right to Work's involvement in past elections when boxes of state candidate files, surveys, mailers and bank statements turned up in 2012 in what authorities described as a Denver "meth house." LeFer said the documents had been stolen. The files were later featured in a "Frontline" documentary that suggested the Right to Work-affiliated group American Tradition Partnership illegally coordinated with candidates.

Last month, Montana Commissioner of Political Practices Jonathan Motl released thousands of additional documents that had been subpoenaed by his office. He declined to comment on their content, citing the pending litigation.

LeFer, who hasn't been accused of wrongdoing and now runs a Denver company that helps nonprofits with regulatory and fundraising compliance, declined to comment. He asked that questions be submitted in an email to which he never replied.

The Virginia-based Right to Work group was created in 1955 and is registered as a 501(c)(4) social welfare organization and its mission says that nobody should be forced to join a union to get or keep a job.

The reason Right to Work ran the mail program was to build relationships with the candidates by providing them with things they can't afford, the group's former field organizer in Iowa, Dennis Fusaro, said in a deposition in November.

"The ability to offer to give someone who doesn't have two nickels to rub together to run for office the ability to do mailings, and if with a wink and a nod they can give them the mail packages, the printed material, the labor to put it together so they can mail the communications and win an election, is value," Fusaro said in the deposition.

His testimony came in a case against Montana state Republican Rep. Art Wittich, who is accused of accepting unreported contributions from Right to Work. A trial is scheduled for March. Wittich has denied the charges.

Among the voter letters was an introductory letter, the wife letter, various letters on issues important to conservative voters of the district and a final letter mailed just before the election, what Fusaro called the "Hail Mary" letter. "My campaign mail strategy is very late-stage, but deadly effective," LeFer said in a pitch to Montana legislative candidates in 2008 and 2010.

Fusaro agreed to that characterization, according his deposition. Fusaro did not respond to an AP query requesting comment.

The program was overseen by Doug Stafford, a former Right to Work vice president who most recently was chief strategist for Kentucky Sen. Rand Paul's presidential campaign. Stafford and former Ron Paul presidential campaign staffer, Dimitri Kesari, oversaw field organizers such as LeFer and Fusaro, according to statements by Fusaro that are supported by emails contained in the documents. The letters' chief copywriter was Jedd Coburn, a former Right to Work staffer who worked on the elder Paul's 2012 presidential bid.

Stafford, Kesari and Coburn did not respond to requests for comment.