Securus Technologies has an exclusive contract to provide the phone service in Cook County Jail. Last year WBEZ reported the company was charging the mostly poor inmates at the jail as much as $15 for 15-minute phone calls.

Since then the county has renegotiated the contract, cutting the costs to inmates.  In the process the county discovered Securus may have been withholding money. The company is supposed to pay 57 and a half percent of the phone revenues to the county. Lydia Murray works for Cook County Board President Preckwinkle and says Securus was levying extra charges on inmates and not giving the county its cut.

“We haven’t been getting these fees and we’ll say that we’re due them and they could be substantial,” said Murray.

The county board is expected to vote on a $290,000 contract today to hire a Louisiana company named Praeses to audit the phone contract and to find places the county is owed money.

Securus didn’t immediately return calls for comment.