Free massages, fancy dinner banquets, and luxurious dinner cruises: These are just a few of the ways in which private prison-company executives woo government officials at industry-sponsored events, says a new report to be released today by In the Public Interest (ITPI), a policy group in Washington, D.C.

For decades, for-profit prison companies have become a powerful force on Capitol Hill, spending millions in lobbying dollars and campaign contributions. We know this because disclosure laws require transparent dealings between private enterprises and public officials. However, those disclosure laws do not apply to a murkier side of the private prison business -- the trade shows and conferences sponsored by corrections associations.

“It’s very much behind the scenes,” said Benjamin Davis, a research analyst at ITPI and author of the report. “They campaign, they lobby, but they also build relationships with officials through these associations. There's definitely a degree of wining and dining.”

ITPI’s 30-page report, “Buying Access: How Corporations Influence Decision Makers at Corrections Conferences, Trainings, and Meetings,” delves into this little-known world, which Davis called a “third avenue of influence” for jail and prison companies. That influence, not surprisingly, can be enormously lucrative.

As the number of inmates around the country has quadrupled over the last 30 years, the for-profit prison industry has boomed. For instance, two of the largest prison operators -- the GEO Group and Corrections Corporation of America (CCA) -- earned a combined $3.3 billion in revenue in 2014. Since 1989, GEO and CCA have spent a combined $25 million in lobbying efforts, government records show.

But lobbying goes only so far.

Sponsorships at jail and prison “events” can give these companies a key introduction to government officials who, in turn, are responsible for buying the goods and services needed to operate their facilities. According to the report, in 2014, private companies contributed at least $3 million to five of the largest professional corrections associations, paying anywhere between $5,000 and $30,000 to get their brand names -- and executives -- front and center. “The millions of dollars spent ... buy the companies opportunities to build their brands and market their products and services to decision makers,” the report notes.

Like any good trade show, there’s some fun stuff, too. Companies do their best to stand out and get noticed. At the 2014 National Sheriff’s Association conference, for instance, Armor Correctional Health Services, a prison and jail medical services company, sponsored a “relaxation station,” where attendees could get neck and shoulder massages. And at the 2014 Michigan Sheriffs’ Association conference, healthcare provider Corizon hosted a dinner cruise, while prison tech firm Securus Technologies co-sponsored the banquet, the report says.

To be sure, there is nothing illegal about these interactions, and they provide a forum for government officials to learn about potentially innovative products and programs being offered by the private sector.

But, as Davis points out, the law currently does not require these corrections associations to offer much, if any, financial transparency around these relationships and events. He believes that should change.

“To achieve full transparency, professional corrections associations should publish complete reports that provide details on the contributions from private companies and the benefits the companies receive in return,” Davis writes in the report. “Only then can the public more fully monitor the influence of corrections companies and protect the public interest.”