WASHINGTON – Federal regulators will vote Friday to overhaul prison phone rates that have skyrocketed, concerned that a few companies are taking advantage of an unregulated corner of the telecommunications industry and isolating convicts from their loved ones.

The rates, which can reach $17 for a 15-minute call, have been a boon for a small set of companies and the prisons that get a share of the money. Many of the phone service providers are privately held and do not disclose revenue.

But their payments to prisons — a fraction of total revenue — reveal a lucrative business dominated by exclusive carriers. Last year alone, prisons in 42 states received $103.9 million in commissions from the phone firms, according to Prison Legal News.

Those arrangements have made it difficult for prisoners to stay in touch with family and friends, prisoner advocates say. The issue was first brought to light 10 years ago by Martha Wright, a District of Columbia resident who petitioned the Federal Communications Commission for reforms when she couldn’t afford to call her grandson in an Arizona prison.

“The cost of calls exploded to as much as $20 for a 15-minute call because of all the fees and charges. My grandmother got to the point where she had to choose between medication or taking our regular Sunday calls,” said Ulandis Forte, 39, who recently returned to join Wright after his 18-year sentence.

Lawmakers, civil rights leaders and hundreds of prisoners and their families have supported Wright’s petition, but the issue languished at the agency until acting FCC Chairman Mignon Clyburn revived it last year.

“This is simply the right thing to do,” Clyburn, a Democrat, said in an interview. She said half of all prisoners live more than 100 miles from their families. Nearly 3 million children have a parent in prison. “Multiple studies have shown that meaningful contact beyond prison walls can make a real difference in maintaining community ties, promoting rehabilitation and reducing recidivism,” she said.

The FCC will vote to limit per-minute rates to 25 cents for long-distance calls so that a 15-minute call can’t exceed $3.75. Extra fees to connect calls also will be banned under the proposed new rules. The new rules, if approved, will go into effect immediately, the agency said.

The agency’s action would upend a pervasive practice in 42 states where a few phone firms have been awarded the lion’s share of prison contracts across the nation with little competition to challenge their rising rates.

In the unregulated market for interstate phone calls from prisons, Global Tel Link, Securus and CenturyLink easily win bids to exclusively provide phone services to prisons with promises to share revenue.

The firms have argued in filings with the FCC that the rates they set for phone calls reflect the higher costs required for added security features.