Jim McAusland has been employed as a consultant by the council since June, to help in the restructuring of its housing department. He was dismissed as chief executive by Boston BC in 1993.
Plaid Cymru group leader Pauline Jarman said: 'The public expect the same high standard of consultants as they do of local government officers and councillors. The Plaid Cymru group will therefore continue to call for the council to sever all ties with this individual immediately.'
It is understood the district auditor has looked into the appointment of Mr McAusland and is happy with it.
On his dismissal from Boston he said: 'I would have taken legal action at the time but my domestic circumstances - my wife was very unwell - didn't permit it. The matter is still in the hands of my legal advisors.'
Mr McAusland has just completed a review of Rhondda Cynon Taff's housing department which he said would save£1.3 million and involve the loss of 60 jobs.