Agricultural Guestworker Act or the AG Act This bill amends the Immigration and Nationality Act to establish a new H-2C nonimmigrant visa for aliens having a residence in a foreign country which they have no intention of abandoning and who are coming temporarily to the United States to perform agricultural labor or services. An employer seeking to employ aliens as H-2C workers must file a petition with the Department of Homeland Security and provide required information. The maximum period of authorized status for temporary or seasonal H-2C workers is 18 months. For aliens not employed as temporary or seasonal workers, the maximum initial period is 36 months with subsequent periods of 18 months. A trust fund is established to provide a monetary incentive for H-2C workers to return to their countries of origin upon expiration of their visas. The bill establishes annual fiscal year H-2C admission limits. The bill also sets forth provisions regarding: (1) penalties for failure to pay wages or required benefits, (2) working conditions and wages, (3) admissions and extensions of stay, (4) abandonment of employment and worker replacement, (5) protection of U.S. workers, and (6) arbitration and mediation of employment-related claims of H-2C workers.