Hassle-free, efficient, simple. These are just a few of the words used by companies that cater to prisons and jails to describe their electronic messaging services, often likened to email for inmates. The service has proliferated in prisons as technology steadily makes its way behind bars, alongside services like electronic tablets and video visitation. Yet without formal regulation by the Federal Communications Commission, the messaging option can come with a hefty price tag for prisoners and their loved ones, according to a new report from the Prison Policy Initiative.

As FCC regulations on exorbitantly priced phone calls to and from prison finally go into effect this year, making calls more affordable, electronic messaging services could take their place as the next revenue opportunity.

“Some of the main companies that have been exploitative in the phone and video visitation industry are the same ones providing electronic messaging,” said Bernadette Rabuy, Prison Policy Initiative’s policy and communications associate. “We’re worried about whether companies are going to see video and electronic messaging as a way to recoup the revenue that they might lose from the regulation of phone calls.”

Though often compared to email, electronic messaging services behind bars are very different in practice. For one, email is generally a free service. These messages are paid for on a per-message basis, sometimes costing as much as $1.25. The service isn’t accessible through traditional email channels such as Gmail—instead, users must log in to a separate website, sometimes requiring its own software. Many of the services only allow inbound messages, which means inmates can receive a message but have to mail a physical letter if they want to reply. In some facilities, Rabuy says, the messages are printed out and handed to inmates.

In December, the FCC published a notice asking for comment from the community on regulatory options for non-telephone communication services in prisons and jails. That request prompted Prison Policy Initiative’s report, as well as feedback from others in the prison advocacy world, such as the Human Rights Defense Center.

In its letter to the FCC, the HRDC affirms Rabuy’s concern that the biggest players in the corrections communications industry are actively seeking new profit avenues beyond phone calls. The letter notes that Securus, one of the three biggest companies that provides these services to prisons and jails, boasted in its 2015 prospectus to investors that it is “expanding into unregulated areas of prison and jail communications in order to increase its profits.”

The comment period closes on Feb. 1, and after that it could be months before the FCC either proposes new rules to regulate the use of video visitation and electronic messaging, or another comment period may open. The battle for fair prices for phone calls to and from prisons was waged for more than a decade before regulations went into effect.