Take context from the input text and decide on the accurate relationship between 'Sergio Marchionne' and 'Fiat' from the options provided.
Options: parent organization, operator, employer, platform

Several months ago, Fiat Chrysler CEO Sergio Marchionne sent Barra an email saying he wanted the two companies to merge, a notion Barra has consistently said she and the company's board of directors are not interested in.
employer