Workers on temporary layoff or on leave who have a reasonable expectation of recall are counted as employees. An employee has a "reasonable expectation of recall" when he/she understands, through notification or through industry practice, that his/her employment with the employer has been temporarily interrupted and that he/she will be recalled to the same or to a similar job. The term "employer" includes non-profit organizations of the requisite size. Regular Federal, State, local and federally recognized Indian tribal governments are not covered. However, the term "employer" includes public and quasi-public entities which engage in business ( i.e. , take part in a commercial or industrial enterprise, supply a service or good on a mercantile basis, or provide independent management of public assets, raising revenue and making desired investments), and which are separately organized from the regular government, which have their own governing bodies and which have independent authority to manage their personnel and assets.
Where 500 or more employees (excluding part-time employees) are affected, the 33% requirement does not apply, and notice is required if the other criteria are met. Plant closings involve employment loss which results from the shutdown of one or more distinct units within a single site or the entire site. A mass layoff involves employment loss, regardless of whether one or more units are shut down at the site.
20 C.F.R. § 639.3