Utilize the input text as a context reference, choose the right relationship between Mary Kay Henry and Service Employees International Union from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Union leaders like American Federation of Teachers President and Service Employees International Union President Mary Kay Henry hitched a ride on Air Force One for the flight to Boston.

Answer: employer