Utilize the input text as a context reference, choose the right relationship between Mary Barra and chief executive officer 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.

GM chief executive officer Mary Barra told reporters in June that she would not negotiate with the UAW in public and preferred to keep any discussions behind closed doors -- a policy both sides have adhered to since talks began last month.
position_held