Mary Kay Henry is an American labor union activist who was elected International President of the Service Employees International Union (SEIU) on May 8, 2010. She is the first woman to lead the union. While serving with the union in California, she helped pioneer SEIU's use of card check agreements, non-traditional collective bargaining agreements, comprehensive campaigns, and system-wide health care organizing strategies. Henry was included on Time's 100 Most Influential People of 2020.