20 C.F.R. § 655.60

An employer may apply for extensions of the period of employment in the following circumstances. A request for extension must be related to weather conditions or other factors beyond the control of the employer (which may include unforeseeable changes in market conditions), and must be supported in writing, with documentation showing why the extension is needed and that the need could not have been reasonably foreseen by the employer. The CO will notify the employer of the decision in writing. Except in extraordinary circumstances, the CO will not grant an extension where the total work period under that Application for Temporary Employment Certification and the authorized extension would exceed 9 months for employers whose temporary need is seasonal, peakload, or intermittent, or 3 years for employers that have a one-time occurrence of temporary need. The employer may appeal a denial of a request for an extension by following the procedures in § 655.61. The H-2B employer's assurances and obligations under the temporary labor certification will continue to apply during the extended period of employment. The employer must immediately provide to its workers a copy of any approved extension.