WARN requires 60 calendar days' written notice. The law makes no provision for any alternative such as pay in place of a notice. While an employer who pays workers for 60 calendar days instead of giving them proper notice technically has violated WARN, the provision of pay and benefits in place of a notice is a possible option. Because WARN provides for back pay and benefits for the period of the violation, up to 60 days, generally this approach by an employer—pay in place of notice—means that the employer has already met the penalty specified in the Act, if the payment is not required to be made. WARN allows voluntary payments of wages and benefits to be offset against any damages that might be awarded.
https://webapps.dol.gov/elaws/eta/warn/faqs.asp#:~:text=An%20employer%20that%20fails%20to,not%20required%20to%20be%20made.