Three top officials from the Oklahoma Tax Commission have agreed to testify before a grand jury investigating wrongdoing at the agency.

Commissioners Thomas Kemp Jr., Jerry Johnson and Donald Kilpatrick are scheduled to appear in December when grand jurors reconvene.

The commission is under investigation for an alleged bribery and kickback scheme involving registration fees paid by out-of-state truckers. Commissioners asked for the investigation last year after discovering problems.

Four former tax commission employees and four trucking agents already have been indicted by the grand jury.

Grand jurors allege the agents pocketed thousands of dollars in trucker fees intended for the state and bribed tax commission employees to aid in the scheme.