Meat Packing Special Investigator Act This bill establishes within the Department of Agriculture's Packers and Stockyards Division the Office of the Special Investigator for Competition Matters. Specifically, the office must use all available tools (e.g., subpoenas) to investigate and prosecute violations of the Packers and Stockyards Act of 1921 by packers. Further, the bill grants the office the authority to bring any civil or administrative action authorized by that act against a packer. Additionally, the office must serve as a liaison to the Department of Justice and the Federal Trade Commission with respect to competition and trade practices in the food and agricultural sector, consult with the Department of Homeland Security on national security and critical infrastructure security in the food and agricultural sector, and maintain a staff of attorneys and other professionals with appropriate expertise.