Immigrants detained at two federal facilities in California have launched a boycott in protest of increasing and, in their view, burdensome prices at the facilities’ commissaries for items including tampons, coffee and soup. The Times reviewed a grievance letter and spoke with three detainees who are involved in the boycott at the California City Detention Facility, about 80 miles east of Bakersfield, and at the Golden State Annex in McFarland. More than 300 detainees are estimated to have signed grievance letters sent recently to facility administrators, according to advocates with the California Collaborative for Immigrant Justice. Both facilities are operated by private prison corporations — the California City facility by Tennessee-based CoreCivic and the Golden State Annex by Florida-based GEO Group. Ryan Gustin, public affairs director for CoreCivic, said the company cares for people at the facility safely, humanely and with dignity while their cases proceed. He said the facility provides three nutritious meals per day and accommodates religious, therapeutic and cultural diets, and that commissary items are a supplement. Proceeds from commissary sales, per …