A six-member investigating committee has held 30 meetings since September to consider serious allegations against Mr Foster raised by the district auditor.
The committee has decided there is sufficient evidence to take the matter further, and an independent adjudicator should be appointed to look at the case.
Concerns raised by auditor Paul Griffiths in a number of reports published in September concerned the appointment of outside consultants, the redevelopment of stately home Dyffryn House and the use of corporate credit cards and hospitality.
The council should consider disciplinary action against Mr Foster and carry out 'a comprehensive trawl' of other contracts, he said.
Mr Griffiths was also critical of the role played by the council's former Labour leader, Shaun Stringer, who is due to appear in court later this month on charges of abuse of public office.
Tony Williams, chairman of the all-party investigating committee, said it had 'left no stone unturned' during the course of its investigation. Its work was continuing, he added. Mr Foster was unavailable for comment.