STROUD, Okla. — An emergency medical services company in Oklahoma has accepted the resignation its CEO amid an ongoing kickback lawsuit.

Stephen Williamson says his retirement from the Emergency Medical Services Authority will take effect on Thursday. Williamson has led the company since 1978. The company manages ambulance services in Oklahoma City and Tulsa.

Williamson recently came under fire after being named in a federal lawsuit that alleges a $20 million kickback scheme involving a Texas contractor.

The authority's board accepted Williamson's resignation on Tuesday. Chief Operating Officer Jim Winham will take over as interim CEO and president.

Williamson's legal expenses associated with the kickbacks lawsuit and another related lawsuit filed by a Tulsa resident will continue to be paid by the company through July. The kickback lawsuit is scheduled for trial July 23.