Retrospective Regularization Of Contractual Employee what is the law

 Temporary on contract basis appointments ware given after obtaining name from employment exchange and following the regular process of selection. Initially the appointments where for 6 months but continued for 20 years uninterruptedly. Appointment was against the vacancies created by the adhoc promotion of existing regular employees to the higher posts who enjoyed their promotion till their retirement. The contractual appointment, said above, was with pay scale and increment. The question is, whether such appointments, as per rule, in such a sanctioned vacancies, can be regularised retrospectively?