Two councils acted unlawfully by letting chief executives opt out of a pension scheme to avoid potential tax payments, the Wales Audit Office says.
Pembrokeshire's Bryn Parry Jones and Carmarthenshire's Mark James had been given cash payments in lieu of employer pension contributions.
Dyfed-Powys Police said the force was in discussions with the auditors.
Calls have been made for resignations or instant dismissals over the matter.
The councils have said they are considering the public spending watchdog report which said that both authorities had acted unlawfully to allow the chief executives to opt out of the Local Government Pension Scheme (LGPS) to avoid potential tax payments.
Mr James was also unlawfully given an indemnity against potential libel costs.
Assistant auditor general Anthony Barrett said: "Carmarthenshire council has acted unlawfully on two fundamental issues, both of which the public need to be fully aware of.
"The authority has taken decisions and used taxpayers money in areas that they do not have the legal powers to do so."