There  is no automatic right to regularization for ad-hoc or temporary teachers, including Associate Professors, even with 20 years of service. Regularization typically requires a proper selection process and adherence to recruitment rules. 

While some cases might involve special consideration due to long service, it's not a universal guarantee. 

Simply completing a certain number of years in an ad-hoc position does not automatically qualify a teacher for regularization. 

Universities usually have specific recruitment rules and procedures for appointing permanent faculty, which often involve open competitions or selection processes. 

The University Grants Commission (UGC) also has guidelines for the appointment and regularization of teachers in universities. 

These guidelines often emphasize the need for a proper selection process. 

While regularization might not be guaranteed, some universities might consider absorbing ad-hoc teachers into the regular cadre if suitable positions become available and they meet the required qualifications and experience. 

In the state of Schttisgarh under The Chattisgarh Regularisatioonof the  emergency appointment rules 2005 under 

Eligibility for Regularisation.

- Such Assistant Professors who have been appointed on Emergency basis and are still working as non selected Assistant Professor shall be eligible for regularisation.Such Assistant Professors of unreserved and reserved categories shall be regularised by relaxing the provisions of column 5 (upper age limit 30 years) of Third Schedule of Chhattisgarh Educational Services (Collegiate Branch) Recruitment Rules, 1990, provided they fulfil the necessary educational qualifications as stipulated in the recruitment rules.

Before seeking all perks and benefits of an Associate Professor your service is required to be regularised, however, the University may  not extend such allowances to ad-hoc staff despite uninterrupted long service.

The remedy lies in approaching the High Court. Though it is a fact the settled law does not favour regularisation of adhoc services, the Apex Court, in its recent decisions has held that the said judgment is not  a shield for denying regularization in public employment and cannot be used to justify exploitative engagements.

The issue can be seen in two parts

1. Seeking Regularisation of service 
2. Restoration of Dearness allowance and other benefits.

The claim for regularisation may not find favour with courts in view of the principles laid down in several cases. Even in a very recent case of regularisation of LIC Class III & IV terminated employees, the Supreme Court court has directed payment of financial compensation in lieu of regularisation.

However the abrupt stoppage of dearness allowance and other benefits can be contested