Salary

As per sec 15(a) under the Head Salary, the following income shall be chargeable to Income Tax :-
(a) Any salary due from an employer to an assessee in the Previous year, WHETHER PAID OR NOT.
My doubt is whether the salary of March which is due to the employee but paid only in April should be taken into account for calculating the income tax of that FY or next FY. Certain Employers are including the salary of March also for deducting TDS of that year as per above Sec(ie
whether paid or not paid). Kindly clear the position.