Salary paid to son

I assume that the father is running a business and his son is assigned with the book-keeping responsibilities of such business, for which he receives a salary.

TDS aspect:

If thats the case, then TDS requirement pretty much depends on whether the estimated salary income received by son exceeds Rs. 2.5 Lakhs during the year. In that case, TDS needs to be made u/s 192 of Income Tax Act, 1961, at the time of payment of such salary. Hence if the son's only income was salary and he if he was not having any Chpt VIA deductions, then ceiling limit would be Rs. 2.5 Lakhs. The rate for TDS would be the Avg rate of income tax based on slab rates.

If the final tax liability of son can be clearly ascertained to be nil, then he may apply for a No-Deduction certificate under Form 15AA with the Assessing officer. Final Tax liability is determined after considering other income, chapter VI deduction and rebate u/s 87A, etc

Cap on Salary to related party:

Now regarding ceiling limit on amount of salary, the father has to keep section 40A(2)(b) in mind while paying salary to son. If the assessing officer is of opinion that such salary is 'excessive' in comparison with the standard industry practices, then the AO has every right to disallow such salary in hands of father. 

Agree with above reply