The Department of Homeland Security and Department of State together come up with a list of countries eligible to use the H-2A and H-2B visa program each year. The 2015 list has just been released, and for the first time, nationals from the Czech Republic, Denmark, Madagascar, Portugal, and Sweden are eligible to participate. A complete list of eligible countries is found here.
The H-2A visa classification allows U.S. employers to bring foreign nationals to the United States to fill seasonal and temporary agricultural jobs for which U.S. workers are not available. The H-2B visa classification allows U.S. employers to bring foreign nationals to the United States to fill temporary non-agricultural jobs for which U.S. workers are not available.