This little-known company is a major funder of right-wing politics. You’ve probably eaten their chicken.

Inside a Maryland chicken factory farm raising animals for Mountaire Farms. | Joseph Allman

At midnight one day in spring 2023, a team of animal rights investigators decked out in biosecurity gear snuck onto a massive chicken farm on Maryland’s Eastern Shore, an hour and a half drive from Baltimore. The operation was raising some 75,000 birds for Mountaire Farms, the nation’s fourth-largest chicken company.

When the investigator Joseph Allman entered one of the facility’s sprawling barns...