Please refer to the section under the Industrial Dispute Act for your ready reference:
25F. Conditions Precedent to Retrenchment of Workmen
No workman employed in any industry who has been in continuous service for not less than one year under an employer shall be retrenched by that employer until:
(a) The workman has been given one month's notice in writing indicating the reasons for retrenchment and the period of notice has expired, or the workman has been paid, in lieu of such notice, wages for the period of the notice;
(b) The workman has been paid, at the time of retrenchment, compensation which shall be equivalent to fifteen days' average pay for every completed year of continuous service or any part thereof in excess of six months; and
(c) Notice in the prescribed manner is served on the appropriate Government or such authority as may be specified by the appropriate Government by notification in the Official Gazette.
*Continuous service of 240 paid days (including week-offs, leaves, and holidays) in a year is considered to be one year of service with the employer.
Hope this helps you to understand.
Regards