Dear Vijay,
No matter that prevous employer has deducted TDS or not u have to deduct TDS on the aggregate salary -by obtaining a declaration from employee duly certified by his previous employer.
The new sub-section (2) inserted in section 192 deals with situations where an individual is working under more than one employer or has changed from one employer to another. It provides for deduction of tax at source by such employer (as the taxpayer may choose) from the aggregate salary of the employee who is or has been in receipt of salary from more than one employer. The employee is now required to furnish to the present/chosen employer details of the income under the head “Salaries” due or received from the former/other employer and also tax deducted at source therefrom, in writing and duly verified by him and by the former/other employer. The present employer will be required to deduct tax at source on the aggregate amount of salary (including salary received from former or other employer). - Circular: No. 504 [F.No. 275/138/87-IT(B)], dated 8-2-1988.
In respect of the emplyee who was employed in Foreign country - Check whether his salary was taxable in India or not, depending upon his residential status..
Further, where employee is claiming that his earlier salary was not taxable, he should be asked to obatin a certificate u/s 197 from his AO