The U.S. Department of Agriculture (USDA) said Friday it had fired dozens of foreign contract workers from China, Russia, North Korea and Iran.The cuts of about 70 workers followed a national security review for U.S. food safety.A USDA spokesperson said the contract workers came from "countries of concern" and will "no longer be able to work on USDA projects."The workers had been with the Agricultural Research Service (ARS), the research arm of the USDA, Thomas Henderson, who represents the union for some of the research workers, told Reuters.TRUMP ADMINISTRATION MOVES DECISIVELY TO BLOCK CHINA FROM 'WEAPONIZING' AMERICAN FARMLANDARS does research on areas of importance to American farmers, such as pests, food safety and climate change. Most of the contract workers were vetted Chinese post-doctoral researchers, with some even arriving to work this week to find out their badges no longer worked.Earlier this month, USDA Secretary Brooke Rollins announced in a new plan to keep U.S. farmland safe that contracts with any workers from China, North Korea, Iran and Russia should be canceled, and nationals from those countries wouldnt be allowed to buy farmland in the U.S.All ARS project publications are also expected to be reanalyzed and those co-authored with researchers from the four countries will be denied, Ethan Roberts, an ARS employee who is also the president of the American Federation of Government Employees Local 3247 union, told Reuters.BROOKE ROLLINS: FARM SECURITY IS NATIONAL SECURITYThe workers wont be able to be replaced until the Oct. 15 federal hiring freeze is lifted.That will force some research projects to be halted, Henderson said, citing a project to develop a vaccine for a deadly toxin that occurs in undercooked beef."We don't have the talent now to progress on these research projects. It's setting us back by years, if not decades," he told Reuters.The agency is down about 1,200 workers through downsizing efforts this year.CLICK HERE TO GET THE FOX NEWS APPFox News Digital has reached out to the USDA for comment.Reuters contributed to this report.