Take context from the input text and decide on the accurate relationship between 'Sergio Marchionne' and 'Fiat' from the options provided.
Options: employer, position held, subsidiary, industry

UAW President Dennis Williams is seeking ratification of the tentative agreement he reached with Fiat Chrysler Chief Executive Officer Sergio Marchionne so he can move on to Ford Motor Co. and General Motors Co. to seek similar, but more lucrative deals.
employer