Seasonal Workers and Applicable Large Employer Status
Under a special rule, companies can exclude certain seasonal workers from their Applicable Large Employer calculations if the employer exceeds 50 employees for four calendar months (or 120 days) or less and the excess for those four months (or 120 days) is caused by seasonal workers. The four months do not have to be consecutive.
The IRS website has additional information on full-time employees and seasonal workers.