The thing is you need to deduct TDS on a retainership bill at 10% in the respective bill he claims, provided the total retainership fee does not exceed Rs. 20K during the financial year. Otherwise, it's not mandatory. Further, professional tax doesn't apply in this case. If you are subject to the deduction of TDS, you may have to remit it to IT on a quarterly basis through form 26A on Q1, Q2, Q3, and Q4 Challans. Finally, issue a TDS Certificate of form 16A, see rule 31(1)(b), to the concerned retainer on an annual financial year basis, showing all payments of retainership along with tax deducted at source to enable him to file his annual return for claiming tax adjustment/refund as the case may be. Hope the above shall suffice your requirements.
Regards,
Devarajan.N