Assistance and Gratitude for Coronavirus Heroes in Agribusiness who are Invaluable to the Nation Act or the AG CHAIN Act This bill allows an exclusion from gross income, for income tax purposes, of wages and other income earned by certain qualified employees for the period between February 15, 2020, and June 15, 2020. The aggregate amount of such exclusion for any such employee may not exceed $25,000. A qualified employee is an essential food and agriculture employee who provides services at grocery stores, gasoline stations, restaurants, and other food service establishments that are located in a county that has at least one confirmed case of COVID-19 (i.e., coronavirus disease 2019). The Department of the Treasury may extend the exclusion period for an additional three months if it determines that the COVID-19 emergency is likely to be ongoing. The bill also suspends the payment of payroll taxes for employee wages not exceeding $75,000 for the same period.