Hundreds of immigrant detainees held in one of the largest detention centers in the U.S. are refusing meals as part of an organized hunger strike, activist groups say.Northwest Detention Center, located on the tidal flats of Tacoma, Washington, at the edge of a toxic EPA Superfund site, has a capacity of 1,575 detainees. It’s operated by giant private prison company the Geo Group.The number of participants in the strike has been fluctuating. Threats of medical intervention, or force-feeding, have discouraged some detainees from continuing, said Maru Mora Villalpando, an activist with the Northwest Immigrants Rights Project. But as of Thursday, about 500 male detainees were taking part. Villalpando said that a group of detained women, who are held in a separate part of the facility from men, learned of the strike and joined, but she was unable to specify how many were participating.Earlier this week, hunger strikers released a list of demands, which included improved medical care, better food, better wages for labor — detainees currently earn $1 a day for working at the facility — speedier court proceedings, and access to educational programs to “keep our heads occupied and avoid depression.”This isn’t the first time detainees at the facility have refused food. In March 2014, advocates said about 1,200 detainees were engaging in a hunger strike to protest against poor working conditions. The following week, President Barack Obama announced that he had ordered the Department of Homeland Security to review his administration’s immigration policies, and met for two hours with 17 immigration reform advocates at the White House.