Utilize the input text as a context reference, choose the right relationship between Buick and Detroit 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.

Buick is planning these production shifts as GM begins contract talks in Detroit with the United Auto Workers.

Answer: headquarters_location