US employers can to hire up to 15,000 extra H-2B workers in coming months. 
The Department of Homeland Security (DHS) determined that “US businesses are in danger of suffering irreparable harm due to a lack of sufficient labor. There are not enough qualified and willing US workers available for temporary non-agricultural jobs.”

The H-2B Temporary Non-Agricultural Worker Program allows US businesses to bring in a maximum of 66,000 temporary foreign workers every year for non-agricultural jobs. (For temporary jobs in agriculture the H-2A program exists.)
A maximum of 33,000 H-2B visas is available during the first half of a Fiscal Year (from October 1 till March 30 the next year). The remaining 33,000 is available in de second half of the FY (from April 1 until September 30).
An H-2B visa can be renewed once, after the second period the worker must leave the US.

For FY 2016 an exemption was in place that effectively quadrupled the number of H-2B visas: returning workers were not counted against the annual statutory cap of 66,000. This provision however was not extended for FY 2017. 

USCIS announced on March 13 it had received sufficient petitions to meet the full statutory cap for FY 2017. Congress gave the Secretary of DHS authority to increase the number. The increase is meant to be a one-time event.

H-2B visas are mainly used in industries with seasonal peaks, e.g. hospitality, tourism & recreation, landscaping, food processing, etc.